Previous research has suggested that hormonal contraceptive users, compared with nonusers, may be at increased risk for acquiring sexually transmitted infections (STIs). We searched the MEDLINE and EMBASE databases for all articles from January 1966 through February 2005 for evidence relevant to all hormonal contraceptives and STIs (including cervical chlamydial and gonococcal infection, human papillomavirus, trichomoniasis, herpes and syphilis). We used standard abstract forms and grading systems to summarize and assess the quality of 83 identified studies. Studies of combined oral contraceptive and depot medroxyprogesterone use generally reported positive associations with cervical chlamydial infection, although not all associations were statistically significant. For other STIs, the findings suggested no association between hormonal contraceptive use and STI acquisition, or the results were too limited to draw any conclusions. Evidence was generally limited in both amount and quality, including inadequate adjustment for confounding, lack of appropriate control groups and small sample sizes. The observed positive associations may be due to a true association or to bias, such as differential exposure to STIs by contraceptive use or increased likelihood of STI detection among hormonal contraceptive users.