To assess the effectiveness of education about cystic fibrosis carrier screening in a primary care setting. Participants were asked to read a brochure, and were offered cystic fibrosis carrier screening. They were assessed for knowledge after reading the brochure and again after having an opportunity to ask questions and reread the brochure at home, at which time consent for testing was obtained. Two sites of a health maintenance organization in the Baltimore, Md, area. Enrollees in a health maintenance organization aged 18 to 44 years. Of 608 enrollees approached, 477 completed an initial knowledge questionnaire, and 143 consented to testing. Change in knowledge score. Knowledge scores improved from a mean of 69% correct initially to 75% at the time of consent (P < 0.1, Student's paired t test). When participants were stratified by educational attainment, significant improvement was observed only for participants with no more than a high school education. However, their final knowledge score was significantly lower than that of college graduates. For people with more formal education, printed materials augmented by a chance to ask questions may be sufficient to ensure informed consent. For less well-educated persons, additional education may be necessary to ensure understanding of difficult concepts.