Since January 25, 1988, the Baltimore City Health Department has offered routine, confidential, human immunodeficiency virus (HIV) testing to clients of the city’s two sexually transmitted disease (STD) clinics. During the first 11 months of the program, testing was offered at 20,843 patient visits and was accepted at 15,181 (73%) of these; 612 (4%) individual clients had results that were positive for HIV. Four hundred thirty-seven (71%) seropositive clients returned for test results, post-test counseling, and further evaluation. Most HIV-in- fected clients were single, and black men accounted for 75% of seropositive individuals. HIV-infected women tended to be younger than infected men (7% of the female clients were adolescents). Although homosexual activity, intravenous drug use, and sex with a partner at risk were common risk factors for seropositive clients, after two interviews 17% of men and 38% of infected women did not report traditional risk factors for HIV infection. Most clients were asymptomatic or had generalized lymphadenopathy at the time of HIV diagnosis. Health care resources for these individuals were limited; 62% of men and 85% of women either had no health insurance or received public assistance. Routine, voluntary, confidential HIV counseling and testing is a practical, effective means to identify HIV-infected individuals among clients being treated at STD clinics. Identification of these individuals early in the course of infection provides opportunities to implement early follow-up and therapy, to counsel clients to help prevent further spread of infection, and to obtain useful information for projecting future health care needs and policy. © 1990 American Sexually Transmitted Diseases Association.