To investigate the impact on sexual behaviour and sexually transmitted infections (STI) of a comprehensive community-led intervention programme for reducing sexual risk among female sex workers (FSW) in Mysore, India. The key programme components were: community mobilization and peer-mediated outreach; increasing access to and utilization of sexual health services; and enhancing the enabling environment to support programme activities. Two cross-sectional surveys among random samples of FSW were conducted 30 months apart, in 2004 and 2006. Of over 1000 women who sell sex in Mysore city, 429 participated in the survey at baseline and 425 at follow-up. The median age was 30 years, median duration in sex work 4 years, and the majority were street based (88%). Striking increases in condom use were seen between baseline and follow-up surveys: condom use at last sex with occasional clients was 65% versus 90%, P < 0001; with repeat clients 53% versus 66%, P < 0.001; and with regular partners 7% versus 30%, P < 0.001. STI prevalence declined from baseline to follow-up: syphilis 25% versus 12%, P < 0.001; trichomonas infection 33% versus 14%, P < 0.001; chlamydial infection 11% versus 5%, P = 0.001; gonorrhoea 5% versus 2%, P = 0.03. HIV prevalence remained stable (26% versus 24%), and detuned assay testing suggested a decline in recent HIV infections. This comprehensive HIV preventive intervention empowering FSW has resulted in striking increases in reported condom use and a concomitant reduction in the prevalence of curable STI. This model should be replicated in similar urban settings across India.