OBJECTIVES: To examine demographic and behavioral characteristics in incarcerated women to determine which characteristics are associated with prevalent sexually transmitted infections (STIs). STUDY DESIGN: A cross-sectional analysis of data of 205 women entering jail in Rhode Island was performed as part of a study evaluating a family planning program. Women were recruited near time of commitment, and inclusion was limited to women at risk for an unplanned pregnancy. Incarcerated women were interviewed by a research assistant for demographic information, psychosocial and behavioral characteristics. Self-collected vaginal swabs were tested for STIs, including Neisseria gonorrhoeae and Chlamydia trachomatis by polymerase chain reaction and Trichomonas vaginalis by InPouch culture. Relative risks (RRs) were estimated using Poisson regression. RESULTS: Sixty-eight of 205 patients tested positive for an STI [33%; 95% confidence interval (CI) 27-40%]. Forty-five patients (26%) tested positive for T. vaginalis, 27 (14%) were positive for C. trachomatis, and 21 (11%) were positive for N. gonorrhoeae. On bivariate analysis, 6 or more sexual partners in the last year (RR 1.84; 95% CI 1.01-3.36), exchanging sex for drugs/money (RR 1.65; 95% CI 1.01-2.69), and homelessness (RR 1.82; 95% CI 1.07-3.09) were associated with STI. After adjustment for age, race/ethnicity, education, and other covariates, none of the factors was significantly associated with STI. CONCLUSIONS: The prevalence of STI in this jail population is high. Incarceration represents a unique opportunity to evaluate and treat this underserved population. Predictors of infection are limited and infection is common; therefore, routine screening should be considered in this population.