Venue-based testing may improve screening efforts for HIV and syphilis, thereby reducing transmission. We offered onsite rapid dual HIV and syphilis testing at venues popular among MSM and/or transgender women in Lima, Peru. We used Poisson regression to calculate adjusted prevalence ratios (aPRs) for factors associated with each infection. Most (90.4%) of the 303 participants would test more frequently if testing was available at alternative venues. New cases of HIV (69) and syphilis infection (84) were identified. HIV was associated with recent sex work (aPR 1.11; 95% CI 1.02–1.22), sex with a partner of unknown serostatus (aPR 1.18; 95% CI 1.09–1.27), exclusively receptive anal sex role (aPR 1.16; 95% CI 1.03–1.30) or versatile sex role (aPR 1.17; 95% CI 1.06–1.30) compared to insertive. Syphilis was associated with reporting role versatility (aPR = 2.69; 95% CI 1.52–5.74). Sex work venues had higher syphilis prevalence 47% versus 28% in other venues, p value = 0.012. Venue-based testing may improve case finding.