OBJECTIVE: To evaluate the type and etiopathogenic role of infectious agents detected in endometrial cultures obtained from women with chronic endometritis (CE). DESIGN: Prospective controlled study. SETTING: University hospital. PATIENT(S): 2190 women undergoing hysteroscopy for different indications. INTERVENTION(S): Vaginal and endometrial samples were collected from 438 women with a CE diagnosis at hysteroscopy and 100 women with no signs of CE (controls). MAIN OUTCOME MEASURE(S): Histology and cultures for common bacteria, Neisseria gonorrhoeae and Mycoplasma, and molecular biology testing for Chlamydia were performed. RESULT(S): We compared results of vaginal and intrauterine cultures obtained from women with and without CE. Histologic results were positive in 388 of these cases (88.6%), and at least one microorganism was found in 320 endometrial samples (73.1%). In the control group, histologic results and endometrial culture were positive in only 6% and 5% of cases, respectively. The most frequent infectious agents detected at the endometrial level were common bacteria (58% of cases). Ureaplasma urealyticum was detected in 10% and Chlamydia in only 2.7% of positive endometrial cultures. In only 143 (32.6%) cases were the same infectious agent isolated in endometrial and vaginal cultures. CONCLUSION(S): More than 70% of CE cases resulted from nongonococcal, nonchlamydial infections. Common bacteria and Mycoplasma were the most frequent etiologic agents. Vaginal cultures have low concordance with endometrial cultures.