OBJECTIVE: To investigate the association between lower genital tract infections and subclinical PID. Fallopian tube damage is a common complication of acute symptomatic pelvic inflammatory disease (PID), yet most women with tubal factor infertility do not have a history of acute PID. Subclinical PID is believed to be an important cause of tubal factor infertility. METHODS: We conducted a cross-sectional study among women attending a sexually transmitted diseases or ambulatory gynecology clinic. A convenience sample of 556 women with bacterial vaginosis, gonorrhea, or chlamydia, or women at risk for gonorrhea or chlamydia were enrolled. Women diagnosed with acute PID were not eligible to participate. The main outcome was subclinical PID, as defined by the presence of histologic endometritis. RESULTS: Subclinical PID was more common in women with lower genital tract infection than in uninfected women. Subclinical PID was present in 27% of women with Chlamydia trachomatis (odds ratio 3.4; 95% confidence interval [CI] 1.8, 6.3) and in 26% of women infected with Neisseria gonorrhoeae (odds ratio 2.4; 95% CI 1.1, 5.1). Among women with bacterial vaginosis, 15% had endometritis (odds ratio 2.7; 95% CI 1.02, 7.2). CONCLUSION: Subclinical PID is common among women with lower genital tract infections. Additional prospective studies are necessary to determine the reproductive impact of these asymptomatic upper genital tract infections.