OBJECTIVE To determine whether pelvic damage is associated with positive Chlamydia trachomatis serology in women with tubal ectopic pregnancy. METHODS Cross-sectional retrospective study. METHODS A prepaid health maintenance organization. METHODS Two-hundred eighty-one women admitted with confirmed tubal ectopic pregnancy were interviewed for history of sexually transmitted diseases. Chlamydia serology was obtained for 135 subjects, and operative findings were available for 121 of these. METHODS None. METHODS Pelvic damage, as determined by review of operative findings of the pelvis at the time of ectopic surgery. RESULTS Pelvic damage was associated with positive chlamydia serology with an adjusted odds ratio of 4.2 (95% confidence interval: 1.8 to 9.7). Moderate and severe pelvic damage were more strongly associated with positive serology than mild damage. CONCLUSIONS Women with ectopic pregnancies and antibodies to C. trachomatis are more likely to have damaged pelves than women with ectopic pregnancies without such antibodies. Prevention or early treatment of C. trachomatis infection may reduce pelvic damage and, therefore, reduce incidence of ectopic pregnancy.