Background In several urban areas globally, reports describe increasing sexually transmitted infection (STI) prevalence attributed to group sex characterised by Internet-based networks and drug use among men who have sex with men (MSM). In Thailand, “high parties” (HPs) (group sex with concomitant drug use) have emerged as possible drivers of STI epidemics among MSM; this analysis aims to describe associated factors.

Methods In the ongoing Bangkok MSM Cohort Study, participants are Thai MSM aged > 18 years followed every 4 months for 60 months for HIV testing and behavioural questionnaire completion. Questions regarding HPs were introduced in April 2010, with analysis limited to men contributing HP data through January 2013. We assessed HP descriptors among attendees using proportions and factors associated with HP attendance using generalised estimating equations.

Results Of 1340 men, prior HP attendance was reported by 207 (15.4%), of whom 161 joined in the previous 4 months. Of recent attendees, 60.3% reported consistent condom use, while 11.7% reported never using condoms at HPs. In a multivariable model, HP attendance in the previous 4 months was independently associated with sex while intoxicated (Adjusted Odds Ratio (AOR) 7.60, 95% CI: 4.43–13.0), methamphetamine (AOR 7.10, 95% CI: 4.15–12.1), gamma hydroxybutyrate (AOR 3.08, 95% CI: 1.15–8.20) and Viagra (AOR 2.35, 95% CI: 1.60–3.43) use, finding partners in Internet chat rooms (AOR 1.56, 95% CI: 1.12–2.27), and sex with casual partners at school/work (AOR 2.61, 95% CI: 1.05–6.53), in a partner’s home (AOR 1.66, 95% CI: 1.20–2.29), or in a hotel (AOR 1.56, 95% CI: 1.12–2.17) in the previous four months.

Conclusions HP attendance is strongly associated with multi-drug use and sex while intoxicated, increasing STI transmission risk. Internet-based education regarding drug use and condoms and non-coitally dependent prevention technologies are urgently needed among MSM in Bangkok.