BACKGROUND: Among women with pelvic inflammatory disease (PID), we assessed the associations among antibodies to Chlamydia trachomatis elementary bodies (EB), antibodies to chlamydia heat shock protein (Chsp60), rates of pregnancy, and PID recurrence. METHODS: Four hundred forty-three women with clinical signs and symptoms of mild to moderate PID enrolled in the PID Evaluation and Clinical Health Study were followed for a mean of 84 months for outcomes of time-to-pregnancy and time-to-PID recurrence. Antibodies to EB and Chsp60 were assessed in relation to these long-term sequelae of PID. RESULTS: Rates of pregnancy were significantly lower (adj. hazard ratio 0.47, 95% confidence interval 0.28-0.79) and PID recurrence higher (adj. hazard ratio 2.48, 95% confidence interval 1.00-6.27) after adjusting for confounding factors among women whose antibody titers to chlamydia EB measured in the final year of follow-up were in the highest tertile. CONCLUSION: Among women with mild to moderate PID, antibodies to C. trachomatis were independently associated with reduced rates of pregnancy and elevated rates of recurrent PID. © Copyright 2008 American Sexually Transmitted Diseases Association.