Background and Objectives: Epidemiologic studies of chlamydial infections may often miss factors associated with the acquisition of infection. Goal: To evaluate factors associated with risk for initial and recurrent Chlamydia trachomatis infections. Study Design: A retrospective study of patients attending a sexually transmitted disease clinic and, within this retrospective cohort, a nested case-control study. Results: Among initial-negative subjects the crude incidence rate was 11.5 per 1,000 months of follow-up. Among initial-positive subjects, the crude incidence rate was 28 per 1,000 months of follow-up (RR = 1.8, 95% CI: 1.4-2.2). The increase in risk of infection associated with prior infection was independent of age. In the case-control study, a reduced risk of recurrent infection was associated with tubal ligation, hormonal contraception, and barrier contraception. Conclusions: As well as targeting sexually active adolescents, prevention programs should recommend repeat testing for all women with prior chlamydial infection, irrespective of age. Furthermore, issues related to personal control of health may modify risk for infection.