Objective. To determine human immunodeficiency virus (HIV) seroprevalence in a sample of men who have sex with men (MSM) in Buenos Aires City and to identify risk factors associated with HIV type 1 infection. Methods. Participants were invited to receive HIV counselling and testing at 'NEXO' (a gay non-governmental organization) by means of informative leaflets distributed in gay nightclubs, porno cinemas, gymnasiums, and in the streets. During the encounter, the study was explained by a trained social worker and individuals were invited to volunteer for the study. Diagnosis of HIV was performed using two screening tests and Western Blot assay was used as confirmatory. Results. Human immunodeficiency virus was detected in 96 (13.8%; 95% CI: 11.4-16.7) of 694 MSM. Fourteen (14.6%) of the 96 HIV-positive MSM were already aware of their HIV serostatus. In univariate analysis, HIV-1 infection (odds ratio [OR] >1.5) was found to be associated with older age (30-39 years), being unemployed, a previous sexually transmitted disease (STD) history, and having an HIV-positive partner. Cocaine consumption and irregular use of condoms with occasional partners were also found to be risk factors. In multivariate logistic regression analysis, being unemployed (OR = 3.42; 95% CI: 1.17-9.99) and having an HIV-positive partner (OR = 2.67; 95% CI: 1.09-6.52) remained significant risk factors. Discussion. The high HIV-1 prevalence observed suggests an urgent need for implementation of effective prevention campaigns. This represents the first cross-sectional epidemiological study of HIV among the high-risk group of MSM in Argentina.