Sixty-eight patients with postpartum endomyometritis were enrolled in this open randomized comparative study. Forty-two patients received ampicillin/sulbactam and 26 received clindamycin. The cure rates were similar in the two groups: 83% in the ampicillin/sulbactam group and 88% in the clindamycin group. The most frequent endometrial bacterial isolates were Bacteroides bivius, Streptococcus faecalis, Escherichia coli, and Ureaplasma urealyticum. Bacteremia was present in 15 of 68 (22%), the most frequent isolates being Mycoplasma (four cases) and B bivius (three cases). Clindamycin-resistant species were S faecalis, E coli, and Proteus mirabilis. There were seven treatment failures in the ampicillin/sulbactam group; only one isolate (an E coli) was resistant to ampicillin/sulbactam. In a significant number of these failures, Mycoplasma was isolated. Ampicillin/sulbactam and clindamycin were found to be equally efficacious in the treatment of postpartum endometritis.