Our purpose was to evaluate the antimicrobial therapy effect on clinical and laboratory findings among women at risk for endometritis.A prospective antimicrobial treatment trial of 153 women was performed to characterize subacute endometritis and to determine the treatment effect on endometritis resolution.After antimicrobial treatment, significant reductions occurred in abnormal bleeding (60% vs 29%), mucopurulent cervicitis (20% vs 6%), uterine tenderness (20% vs 6%), and histologic endometritis (38% vs 4%), all P<.001. In women with prior pelvic inflammatory disease (PID), endometritis was present in 43% with and 28% without current Chlamydia trachomatis or Neisseria gonorrhoeae. In women without prior PID, endometritis was present in 23% with and 12% without current C trachomatis or N gonorrhoeae (P=.002 for trend).In women without a clinical diagnosis of PID, antimicrobial therapy decreased abnormal clinical findings and histologic endometritis. Prior PID is additive with current cervical infection as a risk for endometritis.