This study aimed to determine the prevalence of sexually transmitted infections (STIs) among HIV-infected and uninfected pregnant women in Tanga, Tanzania. Retrospective data on syphilis and HIV status during 2008-2010 were collected from antenatal clinic (ANC) records. Prospective data were collected from HIV-infected (n = 105) and HIV-uninfected pregnant women (n = 100) attending ANCs between April 2009 and August 2010. Syphilis prevalence showed a declining trend (3.1%, 1.4% and 1.3%), while HIV prevalence was stable (6.1%, 6.4% and 5.4%) during 2008-2010. HIV-infected women had significantly higher prevalence of trichomoniasis (18.8% versus 5.0%; P < 0.003) and candidiasis (16.5% versus 2.0%; P < 0.001) while the higher rate of gonorrhoea (3.5% versus 0%; P = 0.095) was not statistically significant when compared with HIV-uninfected women. There were no statistically significant differences in prevalence of chlamydial infection (0% versus 3.0%; P = 0.156) or syphilis (2.4% versus 3.0%; P = 1) between HIV-infected and uninfected women. Other STIs were common in both HIV-infected and uninfected pregnant women.