To determine the specific impact on the incidence rate of some demographic and behavioral characteristics in outpatients with four bacterial sexually transmitted diseases (STDs). A cross-sectional hospital outpatient-based study was conducted from 1990 to 1996 on 1064 consecutive symptomatic STD cases (Chlamydia trachomatis, n = 375; gonorrhea, n = 369; early symptomatic syphilis, n = 288, and chancroid, n = 32) using a standardized questionnaire. In a reference STD population of 5831 symptomatic outpatients, the relative incidence of gonorrhea, syphilis and chancroid was found to be increased among immigrants. Low educational/socioeconomic level was also a significant incidence predictor. Older age characterized homo/bisexuals. The chlamydial infection detection rate was not affected by nationality, injecting drug use history or sexual orientation in males. Innovative preventive and control strategies are needed among immigrants, older men having sex with men and injecting drug users, apart from those targeting the general population.