Studies describing sexually transmitted disease (STD) and human immunodeficiency virus (HIV) prevention practices of primary care physicians have relied on physician or patient reports. This study describes physician STD/HIV prevention practices as observed by unannounced simulated patient evaluators (SPEs). SPEs visited sixty-five primary care physicians. Each SPE portrayed a sexually active female, new to the area, requesting a consultation on STD prevention. One-third of the physicians in the study asked no risk questions, and over 80% failed to ask the SPE specifically about her sexual practices. Most physicians discussed the risks of STDs and HIV and covered basic recommendations (use condoms and know partners better); however, few physicians provided any individualized information or advice about safer sexual practices and the specifics of condom use, such as how to use them or what kind to use. These observations support the low rates of STD/HIV prevention indicated in physicians' self-report and further identify specific deficiencies in the thoroughness of their risk assessment and preventive counseling practices.