The increased hospital stay and direct costs of hospitalization as a result of postcesarean section endometritis were evaluated in a case-matched and controlled study (N = 20 in each group). Endometritis increased postcesarean section hospital stay by 3 days and increased hospital cost by $850. Fifteen to 20% of women delivered by cesarean section develop postpartum endometritis. The success of future antibiotic or surgical intervention studies in reducing this high complication rate can be more accurately evaluated by comparison with these now established parameters of morbidity and cost.