The release of the U.S. Preventive Services Task Force guidelines (GUIDELINES) introduces an opportunity to modify patient expectations about the timing of routine examinations. This randomized, controlled study examines the effect of a materials-based educational intervention on knowledge and beliefs about risk-based preventive screening guidelines. The study was conducted in a large multi-specialty group practice participating in a network model HMO in the upper midwest with over 250,000 members. Subjects were selected from patients of a primary care clinic in a suburban section of a major metropolitan area. A 48-page prevention guidebook based on the GUIDELINES was distributed to a randomly assigned treatment group of 200 patients enrolled in an HMO. A 22-item questionnaire on preventive health services that measured respondents' age-adjusted risks and knowledge of risk-based screening guidelines was sent to both experimental and control groups. A 69% response rate was achieved, χ2analysis and t-tests showed that the treatment group was significantly more accurate in identifying recommended GUIDELINES for colon examinations (digital rectal, stool occult, sigmoidoscopy), blood pressure, and Pap tests. No significant differences related to identifying GUIDELINES for mammograms and clinical breast examinations were found between the groups. Communications about new screening guidelines can yield positive but selective changes in knowledge and beliefs about appropriate screening intervals.