Exhibit 99.1

2Q09 Earnings Release

FOR IMMEDIATE RELEASE

CONTACT:		Investor Relations
		John Eldridge
		(206) 272-6571
		j.eldridge@f5.com
		Public Relations
		Alane Moran
		(206) 272-6850
		a.moran@f5.com

F5 Networks Announces Second Quarter 2009 Results

SEATTLE, April 22, 2009 — F5 Networks, Inc. (NASDAQ: FFIV) today announced revenue of $154.1 million for the second quarter of fiscal 2009, down seven percent from $165.6 million in the first quarter of fiscal 2009 and three percent from $159.1 million in the second quarter of fiscal 2008.

GAAP net income for the second quarter was $19.0 million ($0.24 per diluted share) compared to $21.4 million ($0.27 per diluted share) in the first quarter of 2009 and $17.7 million ($0.21 per diluted share) in the second quarter of fiscal 2008. Excluding the impact of stock-based compensation, a restructuring charge, and a charge for a patent-related legal settlement, non-GAAP net income for the second quarter was $30.3 million ($0.38 per diluted share), compared to $32.3 million ($0.40 per diluted share) in the prior quarter and $28.9 million ($0.35 per diluted share) in the second quarter of fiscal 2008.

A reconciliation of GAAP net income to non-GAAP net income is included on the attached Consolidated Statements of Operations.

“Continued weakening in the global economy impacted sales across all regions,” said John McAdam, F5 president and chief executive officer. “On a year-over-year basis, February sales were particularly slow, and although March sales improved significantly, revenue for the quarter was below our guidance.”

“Despite the challenging economic environment, revenue from our core application delivery controller business was flat as compared to the second quarter of fiscal 2008, and revenue from our file virtualization business grew sequentially from the first quarter of fiscal 2009. We were also pleased that as a result of our aggressive cost-reduction and expense-control initiatives, we exceeded both our operating margin and cash flow targets for the quarter,” McAdam said.

2Q09 Earnings Release

For the third quarter of fiscal 2009, ending June 30, the company has set a revenue target of $148 million to $157 million and a GAAP earnings target of $0.22 to $0.25 per diluted share. Excluding stock-based compensation expense, the company’s non-GAAP earnings target is $0.35 to $0.38 per diluted share. A reconciliation of the company’s expected GAAP and non-GAAP earnings is provided in the following table:

		Three months ended
		June 30, 2009
Reconciliation of Expected Non-GAAP Third Quarter Earnings		Low				High
Net income		$	17.5			$	19.9
Stock-based compensation expense, net of tax		$	10.1			$	10.1
Non-GAAP net income		$	27.6			$	30.0
Net income per share — diluted		$	0.22			$	0.25
Non-GAAP net income per share — diluted		$	0.35			$	0.38

About F5 Networks

F5 Networks is the global leader in Application Delivery Networking (ADN), focused on ensuring the secure, reliable, and fast delivery of applications. F5’s flexible architectural framework enables community-driven innovation that helps organizations enhance IT agility and dynamically deliver services that generate true business value. F5’s vision of unified application and data delivery offers customers an unprecedented level of choice in how they deploy ADN solutions. It redefines how application, server, storage, and network resources are aligned and managed to streamline application delivery and reduce costs. Global enterprise organizations, service providers, and Web 2.0 content providers worldwide trust F5 to keep their business moving forward. For more information, go to www.f5.com.

Forward Looking Statements

Statements in this press release concerning the continuing strength of F5’s business, sequential growth, the target revenue and earnings range, share amount and share price assumptions, demand for application delivery networking and storage virtualization products and other statements that are not historical facts are forward-looking statements. Such forward-looking statements involve risks and uncertainties, as well as assumptions and other factors that, if they do not fully materialize or prove correct, could cause the actual results, performance or achievements of the company, or industry results, to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Such factors include, but are not limited to: customer acceptance of our new traffic management, security, application delivery, WAN optimization and storage virtualization offerings; the timely development, introduction and acceptance of additional new

2Q09 Earnings Release

products and features by F5 or its competitors; competitive pricing pressures; increased sales discounts; uncertain global economic conditions which may result in reduced customer demand for our products and services and changes in customer payment patterns; F5’s ability to sustain, develop and effectively utilize distribution relationships; F5’s ability to attract, train and retain qualified product development, marketing, sales, professional services and customer support personnel; F5’s ability to expand in international markets; the unpredictability of F5’s sales cycle; the share repurchase program; future prices of F5’s common stock; and other risks and uncertainties described more fully in our documents filed with or furnished to the Securities and Exchange Commission. All forward-looking statements in this press release are based on information available as of the date hereof and qualified in their entirety by this cautionary statement. F5 assumes no obligation to revise or update these forward-looking statements.

GAAP to non-GAAP Reconciliation

F5’s management evaluates and makes operating decisions using various operating measures. These measures are generally based on the revenues of its products, services operations and certain costs of those operations, such as cost of revenues, research and development, sales and marketing and general and administrative expenses. One such measure is net income excluding stock-based compensation, which is a non-GAAP financial measure under Section 101 of Regulation G under the Securities Exchange Act of 1934, as amended. This measure consists of GAAP net income excluding, as applicable, stock-based compensation. Net income excluding stock-based compensation (non-GAAP) is adjusted by the amount of additional taxes or tax benefit that the company would accrue if it used non-GAAP results instead of GAAP results to calculate the company’s tax liability. Stock-based compensation is a non-cash expense that F5 has accounted for since July 1, 2005 in accordance with the fair value recognition provisions of Statement of Financial Accounting Standards No. 123(R), “Share-Based Payment.”

Management believes that net income excluding stock-based compensation (non-GAAP) provides useful supplemental information to management and investors regarding the performance of the company’s business operations and facilitates comparisons to the company’s historical operating results. Although F5’s management finds this non-GAAP measure to be useful in evaluating the performance of the business, management’s reliance on this measure is limited because items excluded from such measures could have a material effect on F5’s earnings and earnings per share calculated in accordance with GAAP. Therefore, F5’s management will use its non-GAAP earnings and earnings per share measures, in conjunction with GAAP earnings and earnings per share measures, to address these limitations when evaluating the performance of the company’s business. Investors should consider these non-GAAP measures in addition to, and not as a substitute for, financial performance measures in accordance with GAAP.

The reconciliation of the company’s GAAP and non-GAAP second quarter earnings also excludes a restructuring charge related to a loss on facility exit and workforce reduction and a legal settlement

2Q09 Earnings Release

charge. This restructuring charge was incurred during the second quarter in connection with a reduction in the company’s workforce and the consolidation of certain of the company’s office space.

F5 believes that presenting its non-GAAP measure of earnings and earnings per share provides investors with an additional tool for evaluating the performance of the company’s business, which management uses in its own evaluation of the company’s performance. Investors are encouraged to look at GAAP results as the best measure of financial performance. For example, stock-based compensation is an obligation of the Company that should be considered and each line item is important to financial performance generally. However, while the GAAP results are more complete, the company provides investors this supplemental measure since, with reconciliation to GAAP, it may provide additional insight into its operational performance and financial results.

# # # #

F5 Networks, Inc.
Condensed Consolidated Balance Sheets
(unaudited, in thousands)

		March 31,				September 30,
		2009				2008
Assets
Current assets
Cash and cash equivalents		$	119,688			$	78,303
Short-term investments			138,833				111,883
Accounts receivable, net of allowances of $4,891 and $4,348			90,067				97,057
Inventories			15,036				10,148
Deferred tax assets			5,808				5,910
Other current assets			26,991				20,068
Total current assets			396,423				323,369
Restricted cash, long-term			2,703				2,748
Property and equipment, net			42,852				47,557
Long-term investments			240,572				261,086
Deferred tax assets			44,474				46,917
Goodwill			231,892				231,892
Other assets, net			24,047				25,654
Total assets		$	982,963			$	939,223
Liabilities and Shareholders’ Equity
Current liabilities
Accounts payable		$	20,781			$	13,092
Accrued liabilities			43,225				48,051
Deferred revenue			135,038				125,678
Total current liabilities			199,044				186,821
Other long-term liabilities			13,966				14,822
Deferred revenue, long-term			25,436				19,321
Total long-term liabilities			39,402				34,143
Commitments and contingencies
Shareholders’ equity
Preferred stock, no par value; 10,000 shares authorized, no shares outstanding			—				—
Common stock, no par value; 200,000 shares authorized 78,134 and 79,094 shares issued and outstanding			460,944				477,299
Accumulated other comprehensive loss			(3,872	)			(6,076	)
Retained earnings			287,445				247,036
Total shareholders’ equity			744,517				718,259
Total liabilities and shareholders’ equity		$	982,963			$	939,223

F5 Networks, Inc.
Condensed Consolidated Statements of Operations
(unaudited, in thousands, except per share amounts)

		Three Months Ended								Six Months Ended
		March 31,								March 31,
		2009				2008				2009				2008
Net revenues
Products		$	94,135			$	112,148			$	202,030			$	222,353
Services			60,014				46,993				117,688				90,972
Total			154,149				159,141				319,718				313,325
Cost of net revenues (1)
Products			25,037				24,969				48,960				49,658
Services			11,545				11,719				23,645				22,269
Total			36,582				36,688				72,605				71,927
Gross Profit			117,567				122,453				247,113				241,398
Operating expenses (1)
Sales and marketing			51,933				58,053				111,371				116,231
Research and development			25,977				26,418				53,079				50,750
General and administrative			12,055				14,484				27,860				27,910
Restructuring charges			4,329				—				4,329				—
Total			94,294				98,955				196,639				194,891
Income from operations			23,273				23,498				50,474				46,507
Other income, net			2,136				5,589				5,015				11,721
Income before income taxes			25,409				29,087				55,489				58,228
Provision for income taxes			6,423				11,342				15,080				22,732
Net Income		$	18,986			$	17,745			$	40,409			$	35,496
Net income per share — basic		$	0.24			$	0.21			$	0.51			$	0.42
Weighted average shares — basic			78,925				82,974				79,133				83,919
Net income per share — diluted		$	0.24			$	0.21			$	0.51			$	0.42
Weighted average shares — diluted			79,570				83,805				79,920				85,018
Non-GAAP Financial Measures
Net income as reported		$	18,986			$	17,745			$	40,409			$	35,496
Stock-based compensation expense, net of tax (4)			7,430				11,198				18,337				22,273
Restructuring charges, net of tax (2)			2,957				—				2,957				—
Legal settlement, net of tax (3)			913				—				913				—
Net income excluding stock-based compensation, restructuring charges and legal settlement		$	30,286			$	28,943			$	62,616			$	57,769
Net income per share excluding stock-based compensation, restructuring charges & legal settlement (non-GAAP) — diluted		$	0.38			$	0.35			$	0.78			$	0.68
Weighted average shares — diluted			79,570				83,805				79,920				85,018
(1) Includes stock-based compensation as follows:
Cost of net revenues		$	1,250			$	1,051			$	2,469			$	2,105
Sales and marketing			5,416				6,161				11,383				12,592
Research and development			4,096				4,118				8,382				8,104
General and administrative			2,495				4,337				5,936				8,202
Tax effect of stock-based compensation			(5,827	)			(4,469	)			(9,833	)			(8,730	)
		$	7,430			$	11,198			$	18,337			$	22,273
(2) Includes restructuring charges as follows:
Loss on facility exit		$	2,194			$	—			$	2,194			$	—
Restructuring charges			2,135				—				2,135				—
Tax effect of loss on facility exit and restructuring charges			(1,372	)			—				(1,372	)			—
		$	2,957			$	—			$	2,957			$	—
(3) Includes legal settlement as follows:
Legal settlement		$	1,337			$	—			$	1,337			$	—
Tax effect of legal settlement			(424	)			—				(424	)			—
		$	913			$	—			$	913			$	—

(4) Stock-based compensation is accounted for in accordance with Financial Accounting Standards Board Statement No. 123(R), “Share-Based Payments” using the attribution method for recognizing compensation expense.

F5 Networks, Inc.
Condensed Consolidated Statements of Cash Flows
(unaudited, in thousands)

		Six months ended
		March 31,
		2009				2008
Operating activities
Net income		$	40,409			$	35,496
Adjustments to reconcile net income to net cash provided by operating activities:
Loss (gain) on disposition of assets and investments			13				(31	)
Stock-based compensation			28,170				31,003
Provision for doubtful accounts and sale returns			2,889				1,473
Depreciation and amortization			14,188				11,326
Deferred income taxes			975				219
Gain on auction rate securities put option			(4,177	)			—
Loss on trading auction rate securities			4,177				—
Changes in operating assets and liabilities, net of amounts acquired:
Accounts receivable			4,101				(11,402	)
Inventories			(4,888	)			2,094
Other current assets			(7,066	)			(8,652	)
Other assets			105				(1,323	)
Accounts payable and accrued liabilities			2,755				(3,360	)
Deferred revenue			15,475				22,100
Net cash provided by operating activities			97,126				78,943
Investing activities
Purchase of investments			(166,610	)			(268,448	)
Maturities of investments			163,041				380,306
Investment of restricted cash			22				(4	)
Acquisition of intangible assets			(704	)			—
Acquisition of businesses, net of cash acquired			—				(995	)
Purchase of property and equipment			(6,457	)			(10,438	)
Net cash (used in) provided by investing activities			(10,708	)			100,421
Financing activities
Tax (expense) benefit from nonqualified stock options			(3,002	)			635
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan			5,884				9,492
Repurchase of common stock			(47,437	)			(100,000	)
Net cash used in financing activities			(44,555	)			(89,873	)
Net increase in cash and cash equivalents			41,863				89,491
Effect of exchange rate changes on cash and cash equivalents			(478	)			(1,031	)
Cash and cash equivalents, at beginning of period			78,303				54,296
Cash and cash equivalents, at end of period		$	119,688			$	142,756