The study objective was to estimate the prevalence of selected sexually transmitted infections (STIs) and associated factors among Dhaka slum dwellers. Blood and urine specimens were collected from 1534 men and women. Participants in this cross-sectional study responded to a questionnaire, providing socioeconomic data, symptomatology and treatment-seeking behaviour. Specimens were tested for syphilis, hepatitis B (HBsAg), Neisseria gonorrhoeae, Chlamydia trachomatis, and HIV. Serologic evidence of syphilis infection was found in 6.0% of respondents, HBsAg in 3.8%. Prevalence rates of gonorrhoea and chlamydia were 1.7% and <1%, respectively. No HIV infections were found. Men were more than twice as likely as women to be infected with syphilis or HBsAg carriers. Behaviours facilitating STI transmission were common among men. Syphilis infection is prevalent enough to warrant the initiation of screening programmes in this population. The prevalence rate of hepatitis B carriage suggests that this population would benefit from universal vaccination against hepatitis B.