OBJECTIVE Counseling and testing and partner notification are effective HIV prevention strategies, but they can be resource intensive. This paper evaluates the cost-effectiveness of partner notification and counseling and testing offered in HIV and sexually transmitted disease (STD) clinics in preventing future HIV infections in the United States of America. METHODS Decision trees were developed from both societal and provider perspectives. The counseling and testing and partner notification models incorporate estimates of HIV prevalence, return rates for counseling, risk of HIV transmission within 1 year, and the effectiveness of counseling. Cost estimates for counseling and testing and partner notification programs and lifetime treatment cost of HIV for the United States of America were obtained from published literature. Extensive sensitivity analyses of model parameters were conducted. RESULTS For a cohort of 10,000 individuals at a clinic with an HIV seroprevalence of 1.5%, we estimate that counseling and testing prevents eight HIV infections and saves society almost $1,000,000. We estimate that partner notification for the 113 infected persons identified by counseling and testing, prevents another 1.2 HIV infections and saves an additional $181,000. To the provider (HIV and STD clinics), this translates to a cost of $32,000 per case prevented by counseling and testing and an additional $28,000 for partner notification. Model results are most sensitive to assumptions of HIV prevalence, risk of transmission, and treatment cost of HIV. CONCLUSIONS Counseling and testing and partner notification are cost effective in preventing HIV transmission in this setting. This model can be adapted to assess the cost-effectiveness of counseling and testing and partner notification in other settings.