BACKGROUND: We aimed to describe the current use of antiretrovirals(ARVs) before unprotected anal intercourse (UAI) among Australian gay men, which may represent informal HIV preexposure prophylaxis (PrEP). METHODS: Using data from Australian Gay Community Periodic Surveys conducted in 2011, we assessed the preventive use of ARVs before UAI and its association with sociodemographic characteristics, sexual practices, and drug use in the preceding 6 months. Associations were assessed using multivariate logistic regression analysis. RESULTS: Of 3677 sexually active non-HIV-positive men, 2.5%reported taking ARVs before UAI. The likelihood of ARV use before UAI was significantly higher if any of the following behaviors were also reported: .1 sex partner; UAI with casual partners, irrespective of reporting UAI with regular partners [adjusted odds ratio (AOR) = 2.36; 95% confidence interval (CI): 1.24 to 4.48] or not (AOR = 2.71; 95% CI: 1.44 to 5.07); injecting drugs at least monthly (AOR = 2.56; 95% CI: 1.03 to 6.36); using “party” drugs,occasionally (AOR = 2.23; 95% CI: 1.33 to 3.73) or regularly(AOR = 5.34; 95% CI: 2.99 to 9.56); and group sex while using party drugs, occasionally (AOR = 2.42; 95% CI: 1.29 to 4.53) or regularly (AOR = 5.31; 95% CI: 2.62 to 10.76). Among non-HIV positive men in regular relationships with HIV-positive partners or partners of unknown HIV status, 1.7% and 4.7%, respectively, reported preventive ARV use before UAI. CONCLUSIONS: Our findings illustrate sporadic use of ARVs before UAI among gay men in Australia, which was associated with high-risk casual sex and party drug use. These initial data contribute to a much needed understanding of the informal use of ARVs for HIV prevention.