Five hundred ninety students receiving primary care in a university health service were surveyed anonymously in 1985-86 to study their self-reported sexual behavior and knowledge and attitudes about acquired immunodeficiency syndrome (AIDS). Most students (75%) were heterosexual; 3% were homosexual, 3% bisexual, and 15% had never been sexually active. Many students (32%) had ≥ 2 sexual partners in the past year, but only 23% of these had changed their sexual practices because of concern about AIDS. Some students with high-risk sexual behavior were not very knowledgeable: among homosexual or bisexual men, those with ≥ 6 recent sexual partners knew less than others (P<0.001). Overall, less knowledgeable students had more personal concerns about AIDS, favored limiting the social activities of people infected with human immunodeficiency virus (HIV), and favored screening for HIV-antibody; these associations between knowledge and attitudes were significant even when controlling for demographic characteristics and sexual behavior with multiple linear regression. The authors conclude that many students receiving primary care reported sexual behavior that could spread HIV, and that less knowledgeable students had particular concerns and attitudes about AIDS. © 1988 Society of General Internal Medicine.