A retrospective study by means of multivariant discriminant analysis was performed on 496 deliveries (250 vaginal and 246 cesarean sections) is identify risk factors which predispose to postoperative febrile morbidity, in particular, endometritis. The infection rates for endometritis by type of delivery were: vaginal, 3.6%; elective repeat cesarean section, 6.0%; nonurgent primary cesarean section, 22.2%; and emergency cesarean section, 38.4%. No patient-related risk factors were identified for elective repeat cesarean section, and bacterial isolates were most frequently Staphylococcus aureus. However, four statistically significant risk factors were associated with the occurrence of endometritis after primary cesarean section. In increasing order of significance, they were duration of labor, number of preoperative vaginal examinations, time membranes were ruptured prior to delivery, and postoperative anemia. Internal fetal monitoring was not a risk factor. The clinical relevance of these findings to the use of prophylactic antibiotics and other attempts aimed at decreasing postoperative morbidity is discussed.