The objectives of this paper were to examine changes in AIDS/STD knowledge and behaviour from 1992-1998, current levels of STD infection and psychosocial and demographic determinants of condom use and STD infection among female sex workers. Data for the study were drawn from cross-sectional surveys of female sex workers conducted in 1992, 1994 and 1997-8. For each survey, women participated in a face-to-face interview in the brothel complexes. Survey questions included information on AIDS/STD knowledge, demographics, sexual history and psychosocial factors related to condom use. After the last survey, women were offered a vaginal exam for STD diagnosis and treatment. Sera were tested for HIV infection (anonymous, Elisa/Western blot) and syphilis (TYPHA, RPR). Cervical mucous was tested for chlamydia (LcX), gonorrhea (LCx), herpes (pcr) and HPV (pcr). Knowledge of AIDS and awareness of STDs has increased tremendously in this population since 1992. Reported condom use has also increased substantially (69.9%). Perceived susceptibility toward HIV infection remains low. Ineffective preventive strategies such as medication use continue to be common. HIV infection remains very low in this population (0.2%), although the prevalence of other STDs such as gonorrhea (60.5%), chlamydia (41.3%) and HPV (37.7%) were very high. STD knowledge and self-efficacy were significantly related to condom use as were the sex workers' perceived susceptibility to STD and HIV infection. Women with a larger number of partners were more likely to be infected with gonorrhea, chlamydia and HIV. Women who had come to Bali recently were more likely to be infected with HIV and gonorrhea.