While brothel-based sex work is regulated by the Peruvian government, there is little data on STI risk factors reported by female sex workers (FSW). This study compared high risk behaviors among 120 Peruvian FSW from government regulated brothels with both clients and non-commercial partners. Our study found that 12% of FSW reported unprotected vaginal sex with clients (compared to 75% with non-commercial partners), and 42% reported unprotected anal sex with clients (compared to 87% with non-commercial partners). Group differences were observed in the expectation to have oral sex (32% for partners vs 60% for clients; p<0.01), and a history of anal sex (65% for partners vs 32% for clients; p<0.01) and both vaginal and anal sex with the same partners (46% for partners vs 25% for clients; p<0.001). These findings suggest that FSW constitute an important bridge population for STI/HIV transmission in Peru.