Background: Argentina has a high proportion (32%) of AIDS cases among injecting drug users (IDUs). Few studies show incidence and prevalence in IDUs and in non-injecting drug users (NIDUs). This information is necessary to understand the trend of the epidemic and to design adequate responses. Part of the study was funded by The Global Fund (Sub-Project N°112). Estimate HIV seroprevalence and seroincidence among current drug users (IDUs and NIDUs) in the Buenos Aires Metropolitan Area and to understand the association with their sexual and drug use practices. Methods: Between Oct2006/Oct2007, 358 current cocaine/amphetamine users were recruited; 53% were recruited in drug treatment centers and 47% through harm reduction programs in the neighborhoods were they live. Informed consent, a structured questionnaire and HIV diagnosis and counseling were carried out. Seroincidence was calculated through the detune assay. Results: Sample was 62% male; mean age: 30 years old. HIV Prevalence: 6.7% (95% CI 4.4-9.6) without difference by sex. In a bivariate analyses, variables associated with high level of prevalent infection (OR>1) were: IDUs in last year: 6.5 (1.9-22.5); anal sex between men in last year: 5.4 (2.0-14.4); over 25 years old: 7.6 (1.8-33.0) HIV seroincidence was 3.2 per 100 person-years at risk (95% CI 1.7-5.7) without difference by sex. All recent infections were among non-injecting drug users, 50% among men with history of MSM and 50% among women. Conclusions: Variables associated with high rate of prevalent infection were previous experience with injection drug use, unprotected anal sex among men, and greater age. It is necessary to understand more about sexual and drug use practices among non-injecting drug users in order to develop adequate prevention strategies.