OBJECTIVE: To assess clinic- and community-based trends in demographic and behavioral characteristics and clinic-based trends in HIV infection and other sexually transmitted diseases (STD) in female sex workers in Abidjan, Côte d'Ivoire. DESIGN: Multiyear cross-sectional study of first-time attenders in Clinique de Confiance, a confidential STD clinic; biannual community-based behavioral surveys. METHODS: From 1992 to 1998, female sex workers were invited to attend Clinique de Confiance, where they were counseled, interviewed, clinically examined during their first visit and tested for STD and HIV infection. Community-based surveys, conducted in 1991, 1993, 1995, and 1997, interviewed women regarding socio-demographic characteristics and HIV/STD-related knowledge, attitudes and behavior. RESULTS: Among female sex workers in Abidjan, there was a trend toward shorter duration of sex work, higher prices, and more condom use. Among sex workers attending Clinique de Confiance for the first time, significant declines were found in the prevalence of HIV infection (from 89 to 32%), gonorrhoea (from 33 to 11%), genital ulcers (from 21 to 4%), and syphilis (from 21 to 2%). In a logistic regression model that controlled for socio-demographic and behavioral changes, the year of screening remained significantly associated with HIV infection. CONCLUSION: The increase in condom use and the decline in prevalence of HIV infection and other STD may well have resulted from the prevention campaign for female sex workers, and such campaigns should therefore be continued, strengthened, and expanded.