BACKGROUND Until recently, epidemiologic studies of sexually transmitted diseases (STDs), including human immunodeficiency virus type-1 (HIV-1) infection, among Japanese female commercial sex workers and their patterns of condom use have been rare. We investigated trends in STDs among female commercial sex workers and their condom use patterns in Fukuoka, Japan, from 1990 through 1995. METHODS The study group consisted of 1218 female commercial sex workers who attended an STD clinic to undergo screening for major STDs including chlamydial infection, gonorrhea and HIV-1 infection from 1990 through 1995. Endocervical smear specimens were taken from the women to detect Chlamydia trachomatis and Neisseria gonorrhoeae, and blood samples were obtained for the serologic diagnosis of HIV-1. Also, the commercial sex workers were interviewed concerning their condom use patterns. RESULTS The annual infection and detection rates of C. trachomatis declined significantly from 58.1% in 1990 to 46.2% in 1995 and from 16.3% in 1990 to 10.0% in 1995, respectively, while the annual infection and detection rates of N. gonorrhoeae also declined significantly from 13.2% in 1990 to 3.5% in 1995 and from 1.5% in 1990 to 0.4% in 1995, respectively. None were found to be seropositive for HIV-1 during the 6-year period. The proportion of commercial sex workers using condoms significantly increased during 1992-1993 and 1994-1995 periods, as compared with the 1990-1991 period. CONCLUSIONS Reductions in the prevalence of major STDs among female commercial sex workers may be related to an increase in the frequency of condom use.