This study was conducted to determine the risk factors for recent (active) syphilis among HIV-1 seropositive pregnant women (N = 1058) in Dar es Salaam, Tanzania, Recruitment of study participants (N = 1058) was done between April 1995 and June 1997 at four main prenatal clinics in Dar es Salaam city. Study subjects were interviewed to obtain information about potential risk factors, and blood and genital specimens were collected for detection of syphilis and other genital infections. The prevalence of active syphilis was 5.9%. After adjusting for other risk factors, women without their own source of income had a 50% lower risk of syphilis (OR = 0.5, 95% CI: 0.3-0.9). The risk of active syphilis was significantly increased among women with genital ulceration on examination (OR = 8.4, 95% CI: 1.5-47.7), and in those with trichomoniasis (OR = 2.2, 95% CI: 1.2-3.8). HIV-related immunodeficiency was not associated with increased risk of syphilis. These results show that syphilis and other genital infections are a major problem among HIV infected women. Prevention of syphilis and other genital infections is urgently needed in this population.