The degree and depth to which primary care physicians counsel patients at risk for human immunodeficiency virus (HIV) infection is a major concern. To determine which factors influence whether physicians counsel patients at risk for HIV, primary care physicians’ clinical experience, knowledge, attitudes, and preventive counseling advice in hypothetical case scenarios were assessed. Ninety-nine adult primary care physicians in the Washington, D.C., metropolitan area were interviewed by telephone from May through November 1987. Ninety-one physicians had tested or referred patients for HIV antibody tests. However, 58% could not name the ELISA or Western blot as the tests. The most frequent HIV prevention recommendations were using condoms (67.7%), abstaining from sexual activity (36.4%), getting tested for HIV (30.3%), and safe sex (23.2%). Naming the HIV antibody tests was the most significant predictor of preventive counseling advice; other significant predictors included physicians’ personal comfort with counseling homosexual patients and various physician practice and demographic characteristics. Previous studies showed that homophobia was the main inhibitor of effective AIDS counseling. These results suggest that physicians’ lack of knowledge and general discomfort in counseling patients about sexual risk factors, rather than homophobia alone, are important barriers to preventive counseling about HIV infection.