WASHINGTON, D.C., May 23, 2005 - Cogent Communications Group, Inc. (AMEX: COI), today announced that it intends to raise $75 million through the sale of shares of common stock in an underwritten public offering. The underwriters will have an option to purchase up to an additional 15% of the shares offered to cover over-allotments, if any.

Lehman Brothers is acting as the sole book-running manager, Thomas Weisel Partners is acting as co-lead manager and CIBC World Markets and Friedman Billings Ramsey are acting as co-managers.

This press release does not constitute an offer to sell or the solicitation of an offer to buy any of the securities nor shall there be any sale of these securities in any state in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of such state. A registration statement relating to these securities has been filed with the Securities and Exchange Commission but has not yet become effective. These securities may not be sold nor offers to buy be accepted prior to the time the registration statement becomes effective.

Copies of the prospectus supplement and the accompanying prospectus can be obtained from:

Lehman Brothers Inc.

c/o ADP Financial Services

Prospectus Fulfillment

1155 Long Island Avenue

Edgewood, NY 11717

Thomas Weisel Partners LLC

One Montgomery Tower

One Montgomery Street

San Francisco, CA 94104

CIBC World Markets

USE Prospectus

622 3rd Avenue, 9th Floor

New York, NY 10017

Fax: 212-667-6303

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Friedman Billings Ramsey

1001 Nineteenth Street North

Arlington, VA 22209

About Cogent Communications Group, Inc.

Cogent Communications (AMEX: COI) is a multinational, Tier 1 facilities-based ISP that specializes in providing businesses with high speed Internet access and point-to-point transport services. Cogent's facilities-based, all-optical IP network backbone spans 11 countries and provides IP services in markets located in North America and Europe.

Since Cogent's inception, Cogent has exploited the benefits that IP technology provides, building a network that enables Cogent to offer large, dedicated bandwidth connections at highly competitive prices. Network ownership also enables Cogent to offer superior customer support through the ability to control service delivery and network monitoring end-to-end.

Cogent Communications is headquartered at 1015 31st Street, NW, Washington, D.C. 20007.

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Information in this release may involve expectations, beliefs, plans, intentions or strategies regarding the future. These forward-looking statements involve risks and uncertainties. All forward-looking statements included in this release are based upon information available to Cogent Communications Group, Inc. as of the date of the release, and we assume no obligation to update any such forward-looking statement. The statements in this release are not guarantees of future performance and actual results could differ materially from our current expectations. Numerous factors could cause or contribute to such differences. Some of the factors and risks associated with our business are discussed in Cogent's registration statements filed with the Securities and Exchange Commission and in its other reports filed from time to time with the SEC.

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