Given the extensive use of the Internet for health information, Web-based health promotion interventions are widely perceived as an effective communication channel. The authors conducted this study to determine use of a Web-based intervention intended to improve colorectal cancer screening in a population of women who are at average risk and noncompliant to current screening recommendations. The study was a randomized controlled trial designed to compare the effectiveness of colorectal cancer screening educational materials delivered using the Internet versus a printed format. In 3 years, 391 women seen for routine obstetrics/gynecology follow-up at 2 academic centers provided relevant survey information. Of these, 130 were randomized to the Web intervention. Participants received voluntary access to a password-protected, study-specific Web site that provided information about colorectal cancer and colorectal cancer screening options. The main outcome measures were self-reported and actual Web site use. Only 24.6% of women logged onto the Web site. Age was the only variable that differentiated users from nonusers (p = .03). In contrast, 16% of participants self-reported Web use. There was significant discordance between the veracity of actual and self-reported use (p = .004). Among true users, most (81%) logged on once only. These findings raise questions about how to increase use of important health communication interventions.