Introduction Unprotected sexual intercourse (USI) is a known risk factor for HIV infection. And bisexual men (BSM) who engage in USI with casual and commercial partners may be at a higher risk. Our aim is to estimate prevalence of men having sex with men (MSM), BSM, and USI to guide prevention via sexual route among polysubstance users (PSUs).

Methods A total of 3.449 PSUs were recruited in a cross-sectional study in 10 Brazilian cities through respondent driven sampling in 2009. Data was collected using audio computer-assisted self-interview. Estimates were weighted by the inverse of the participant’s social network size.

Results Among 2,682 (73.7% of the sample) males, 4.4% referred having sex only with men (MSM), 16.2% with both men and women (BSM). 64.8% engaged in USI with commercial partnerships; whereas 47.1% of those exchanged sex for money/drugs 12 months before the interview. Casual partnerships 12 months before the interview were reported by 47.9% of men; whereas 62.3% of those reported USI with that casual partners.

Conclusion It is urgent to design interventions among males PSUs in Brazil who engage in commercial and casual USI. Social interventions, education in health, and linkage to health services are needed to prevent sexual transmission of HIV in this group most at risk.

Disclosure of interest statement This study was funded by the Brazilian Ministry of Health/Department of SDT/AIDS and viral hepatitis, with technical advisor from CDC Brazil. The first author is supported by a grant from the Brazilian National Research Council (CNPq) for his PhD studies.