To evaluate the prevalence of and associated factors for recurrent Chlamydia trachomatis infection in pregnant women, a retrospective cohort study was conducted in an urban prenatal clinic in an underserved area. Women with chlamydial carriage in pregnancy between 1992 and 1996 were identified by a direct DNA assay. Entrance criteria limited the population to those who were positive for chlamydia, were treated, had proof of cure and had at least one subsequent test for chlamydia, all in the same pregnancy. Of the 149 women who met entrance criteria, 25 (17%) had recurrent chlamydial carriage. The only identified risk factor was maternal age <20 years (21 of 98 vs. 4 of 51, odds ratio = 3.21). Infection with gonorrhea or other sexually transmitted diseases during the same pregnancy were not predictive of reinfection. Initial therapy with azithromycin, when compared to erythromycin, did not appear protective for recurrent infection. Pregnant adolescents are more likely to have recurrent chlamydial infection. Prenatal care programs should consider this when counseling and treating these patients.