CDW Corporation will file with the Securities and Exchange Commission (the “SEC”), and furnish to
its shareholders, a proxy statement soliciting proxies for the meeting of its shareholders to be
called with respect to the proposed merger between CDW and Madison Dearborn Partners, LLC. CDW
SHAREHOLDERS ARE ADVISED TO READ THE PROXY STATEMENT WHEN IT IS FINALIZED AND DISTRIBUTED TO THEM
BECAUSE IT WILL CONTAIN IMPORTANT INFORMATION. CDW shareholders and other interested parties will
be able to obtain, without charge, a copy of the proxy statement (when available) and other
relevant documents filed with the SEC from the SEC’s website at http://www.sec.gov. CDW
shareholders and other interested parties will also be able to obtain, without charge, a copy of
the proxy statement (when available) and other relevant documents by directing a request by mail or
telephone to CDW Corporation, 200 N. Milwaukee Ave., Vernon Hills, Illinois 60061, Attention:
Corporate Secretary, telephone: (847) 465-6000, or from CDW’s website, http://www.cdw.com.
CDW and certain of its directors, executive officers and other members of management and employees
may, under SEC rules, be deemed to be “participants” in the solicitation of proxies from
shareholders of CDW with respect to the proposed merger. Information regarding the persons who may
be considered “participants” in the solicitation of proxies will be set forth in CDW’s proxy
statement relating to the proposed merger when it is filed with the SEC. Information regarding
certain of these persons and their beneficial ownership of CDW common stock as of March 31, 2007 is
also set forth in CDW’s proxy statement for its 2007 Annual Meeting of Shareholders, which was
filed with the SEC on April 16, 2007.
Statements about the expected timing, completion and effects of the proposed merger between CDW and
Madison Dearborn Partners, LLC, and all other statements in this filing other than historical
facts, constitute forward-looking statements within the meaning of the safe harbor provisions of
the Private Securities Litigation Reform Act of 1995. Readers are cautioned not to place undue
reliance on these forward-looking statements, each of which is qualified in its entirety by
reference to the following cautionary statements. Forward-looking statements speak only as of the
date hereof and are based on current expectations and involve a number of assumptions, risks and
uncertainties that could cause actual results to differ materially from those projected in the
forward-looking statements. CDW may not be able to complete the proposed merger because of a
number of factors, including, among other things, the failure to obtain shareholder approval, the
failure of financing or the failure to satisfy other closing conditions. Other risks and
uncertainties that may affect forward-looking statements are described in the reports filed by CDW
with the SEC under the Securities Exchange Act of 1934, as amended, including without limitation
CDW’s Annual Report on Form 10-K for the year ended December 31, 2006.
