Exhibit 99.1

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 Results for Third Quarter of Fiscal 2009

SEATTLE, WA—July 22, 2009— For the third quarter of fiscal 2009, F5 Networks, Inc. (NASDAQ: FFIV) announced revenue of $158.2 million, up 2.6 percent from $154.1 million in the prior quarter and down 4.4 percent from $165.6 million in the third quarter of fiscal 2008.

GAAP net income was $22.8 million ($0.29 per diluted share), compared to $19.0 million ($0.24 per diluted share) in the prior quarter and $19.1 million ($0.23 per diluted share) in the third quarter a year ago.

Excluding the impact of stock-based compensation net of tax, non-GAAP net income was $31.9 million ($0.40 per diluted share), compared to $30.3 million ($0.38 per diluted share) in the prior quarter and $30.2 million ($0.37 per diluted share) in the third quarter of fiscal 2008.

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

“While it is still too early to say that the worst is behind us, customer buying patterns did appear to stabilize during the third quarter,” said John McAdam, F5 president and chief executive officer.

“As a result, we were able to grow revenue sequentially and exceed our revenue target. Coupled with better top-line performance, modest gross margin improvement and ongoing expense controls further improved our non-GAAP operating margin and enabled us to exceed both our GAAP and non-GAAP earnings targets as well,” McAdam said.

During the third quarter, the company continued to strengthen its balance sheet, increasing deferred revenue 6 percent to $170 million and generating $46 million in cash flow from operations. After repurchasing another $15.9 million of the company’s outstanding common stock, F5 ended the quarter with $538 million in cash and investments.

Acknowledging that weakness and uncertainty in the global economy persist, McAdam said he is encouraged by the company’s third quarter results. For the current quarter, management has set a revenue goal of $160 million to $164 million with a GAAP earnings target of $0.26 to $0.28 per diluted share. Excluding stock-based compensation expense, the company’s non-GAAP earnings target is $0.40 to $0.42 per diluted share. A reconciliation of the company’s expected GAAP and non-GAAP earnings is provided in the following table:

		Three months ended
		September 30, 2009
Reconciliation of Expected Non-GAAP Fourth Quarter Earnings		Low				High
Net income		$	20.6			$	22.2
Stock-based compensation expense, net of tax		$	11.0			$	11.0
Non-GAAP net income excluding stock-based compensation expense		$	31.6			$	33.2
Net income per share — diluted		$	0.26			$	0.28
Non-GAAP net income per share — diluted		$	0.40			$	0.42

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 the management of application, server, storage, and network resources, streamlining application delivery and reducing costs. Global enterprise organizations, service and cloud providers, and Web 2.0 content providers 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 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.

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)

		June 30,				September 30,
		2009				2008
Assets
Current assets
Cash and cash equivalents		$	88,289			$	78,303
Short-term investments			175,780				111,883
Accounts receivable, net of allowances of $4,273 and $4,348			91,635				97,057
Inventories			13,590				10,148
Deferred tax assets			5,827				5,910
Other current assets			26,324				20,068
Total current assets			401,445				323,369
Restricted cash			2,731				2,748
Property and equipment, net			40,237				47,557
Long-term investments			273,861				261,086
Deferred tax assets			43,982				46,917
Goodwill			231,892				231,892
Other assets, net			23,440				25,654
Total assets		$	1,017,588			$	939,223
Liabilities and Shareholders’ Equity
Current liabilities
Accounts payable		$	16,386			$	13,092
Accrued liabilities			43,080				48,051
Deferred revenue			142,699				125,678
Total current liabilities			202,165				186,821
Other long-term liabilities			13,838				14,822
Deferred revenue, long-term			27,173				19,321
Total long-term liabilities			41,011				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 78,515 and 79,094 shares issued and outstanding			467,391				477,299
Accumulated other comprehensive loss			(3,200	)			(6,076	)
Retained earnings			310,221				247,036
Total shareholders’ equity			774,412				718,259
Total liabilities and shareholders’ equity		$	1,017,588			$	939,223

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

		Three Months Ended								Nine Months Ended
		June 30,								June 30,
		2009				2008				2009				2008
Net revenues
Products		$	95,619			$	114,786			$	297,649			$	337,139
Services			62,612				50,799				180,300				141,771
Total			158,231				165,585				477,949				478,910
Cost of net revenues (1)
Products			21,955				26,158				70,915				75,816
Services			11,710				12,020				35,355				34,289
Total			33,665				38,178				106,270				110,105
Gross Profit			124,566				127,407				371,679				368,805
Operating expenses (1)
Sales and marketing			55,427				60,483				166,798				176,714
Research and development			25,070				26,277				78,149				77,027
General and administrative			12,764				13,459				40,624				41,369
Restructuring charges			—				—				4,329				—
Total			93,261				100,219				289,900				295,110
Income from operations			31,305				27,188				81,779				73,695
Other income, net			3,027				3,716				8,042				15,437
Income before income taxes			34,332				30,904				89,821				89,132
Provision for income taxes			11,556				11,770				26,636				34,502
Net Income		$	22,776			$	19,134			$	63,185			$	54,630
Net income per share — basic		$	0.29			$	0.24			$	0.80			$	0.66
Weighted average shares — basic			78,603				81,096				78,958				83,218
Net income per share — diluted		$	0.29			$	0.23			$	0.79			$	0.65
Weighted average shares — diluted			79,612				81,951				80,014				84,308
Non-GAAP Financial Measures
Net income as reported		$	22,776			$	19,134			$	63,185			$	54,630
Stock-based compensation expense, net of tax (4)			9,157				11,037				27,494				33,310
Restructuring charges, net of tax (2)			—				—				2,957				—
Legal settlement, net of tax (3)			—				—				913				—
Net income excluding stock-based compensation, restructuring charges and legal settlement		$	31,933			$	30,171			$	94,549			$	87,940
Net income per share excluding stock-based compensation, restructuring charges & legal settlement (non-GAAP) — diluted		$	0.40			$	0.37			$	1.18			$	1.04
Weighted average shares — diluted			79,612				81,951				80,014				84,308
(1)    Includes stock-based compensation as follows:
Cost of net revenues		$	1,211			$	1,065			$	3,680			$	3,170
Sales and marketing			5,136				5,846				16,519				18,438
Research and development			3,816				4,116				12,198				12,220
General and administrative			2,394				3,790				8,330				11,992
Tax effect of stock-based compensation			(3,400	)			(3,780	)			(13,233	)			(12,510	)
		$	9,157			$	11,037			$	27,494			$	33,310
(2)    Includes restructuring charges as follows:
Loss on facility exit		$	—			$	—			$	2,194			$	—
Restructuring charges			—				—				2,135				—
Tax effect of loss on facility exit and restructuring charges			—				—				(1,372	)			—
		$	—			$	—			$	2,957			$	—
(3)    Includes legal settlement as follows:
Legal settlement		$	—			$	—			$	1,337			$	—
Tax effect of legal settlement			—				—				(424	)			—
		$	—			$	—			$	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)

		Nine months ended
		June 30,
		2009				2008
Operating activities
Net income		$	63,185			$	54,630
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on disposition of assets and investments			20				18
Stock-based compensation			40,727				45,820
Provisions for doubtful accounts and sale returns			2,552				1,887
Depreciation and amortization			20,432				17,362
Deferred income taxes			1,352				478
Gain on auction rate securities put option			(3,788	)			—
Loss on trading auction rate securities			3,788				—
Changes in operating assets and liabilities, net of amounts acquired:
Accounts receivable			2,869				(8,083	)
Inventories			(3,442	)			1,009
Other current assets			(6,201	)			(5,595	)
Other assets			(512	)			(1,673	)
Accounts payable and accrued liabilities			(2,490	)			(9,554	)
Deferred revenue			24,873				38,448
Net cash provided by operating activities			143,365				134,747
Investing activities
Purchases of investments			(329,694	)			(421,697	)
Maturities of investments			256,091				500,672
Investment of restricted cash			5				—
Acquisition of intangible assets			(706	)			—
Acquisition of businesses, net of cash acquired			—				(995	)
Purchases of property and equipment			(8,232	)			(23,201	)
Net cash (used in) provided by investing activities			(82,536	)			54,779
Financing activities
Tax expense from nonqualified stock options			(2,758	)			(664	)
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan			15,326				17,075
Repurchase of common stock			(63,311	)			(150,000	)
Net cash used in financing activities			(50,743	)			(133,589	)
Net increase in cash and cash equivalents			10,086				55,937
Effect of exchange rate changes on cash and cash equivalents			(100	)			(1,049	)
Cash and cash equivalents, beginning of period			78,303				54,296
Cash and cash equivalents, end of period		$	88,289			$	109,184