Exhibit 99.1

FOR IMMEDIATE RELEASE

F5 Networks Announces Fiscal First Quarter Results

Strong revenue growth drives improved profitability

SEATTLE, WA—January 21, 2004 —F5 Networks today announced net income of $3.8 million ($0.11 per diluted share) on revenue of $36.1 million for the first quarter of fiscal 2004, up from $1.4 million ($0.05 per diluted share) on revenue of $31.6 million in the fourth quarter of 2003. In the first quarter of fiscal 2003 the company reported net income of $0.5 million ($0.02 per diluted share) on revenue of $27.1 million.

F5 president and chief executive officer John McAdam said the company’s strong performance reflected continuing strength in its core traffic management business across all geographic regions and product lines, which helped boost its first quarter operating margin to 11 percent. Year over year, product revenue grew 35 percent while service revenue increased 28 percent during the same period. In addition, McAdam said sales of the company’s recently acquired FirePass SSL VPN technology were stronger than anticipated, accounting for more than 5 percent of product sales.

“During the past several quarters we’ve seen increasing returns from our ongoing investments in product development and our focus on enterprise customers,” McAdam said. “Growing demand for our core products and services is evidence that enterprises are increasingly aware of the benefits of application traffic management in general and the advanced features and functionality that have made BIG-IP a technology and market leader.”

In addition to its strong operating results, McAdam said the company continued to strengthen its balance sheet during the quarter. Days sales outstanding (DSO) fell to 44 days, contributing to positive cash flow of $8.4 million from operations. At December 31, 2003, the company had $205.0 million in cash, cash equivalents and investments, including $113.6 million from its recently completed public offering. For the second quarter of fiscal 2004, McAdam said management believes the company will continue to grow sequentially and has set a target range of $37.0 million to $39.0 million in revenue with net income of $0.13 to $0.15 per share.

F5 Networks Announces Fiscal First Quarter Results

About F5 Networks

F5 Networks keeps IP-based traffic flowing and business information always available to any user from any device, anywhere in the world. Our products ensure secure and reliable access to servers and the applications that run on them. F5 also provides tools to automate communications between applications and the network, eliminating tedious, manual processes.

As the pioneers of intelligent load balancing, F5’s continued innovations help businesses optimize and protect their IT investments. Our mission is to ensure the availability, scalability, performance, and security of IT resources that enterprises require to successfully do business. The company is headquartered in Seattle, Washington, with offices worldwide. For more information go to www.f5.com.

Forward Looking Statements

Statements in this press release concerning sequential growth, revenue, earnings and net income targets for the second quarter of fiscal 2004 and other statements that are not historical facts are forward-looking statements. Such forward-looking statements involve known and unknown risks, uncertainties and other factors which may cause the actual results, performance or achievements of F5, 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, among others: acceptance of F5’s products, the timely development, introduction and acceptance of additional new products and features by F5 or its competitors; competitive pricing pressures; increased sales discounts; F5’s ability to sustain or develop 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 the international markets and the unpredictability of F5’s sales cycle. F5 has no duty to update any guidance provided. More information about potential risk factors that could affect F5’s business and financial results is included in F5’s annual report on Form 10-K for the fiscal year ended September 30, 2003, and other public filings with the Securities and Exchange Commission.

# # #

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

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