Studies examining the increased surgical morbidity among obese gravidas have focused mainly on differences in outcome between obese and nonobese mothers. Little is known, however, about the cause for worsened operative outcome in obese mothers or the potential impact of perioperative interventions. To define more precisely the clinical determinants of postoperative morbidity, multivariate analysis was used to relate antepartum and intrapartum variables to three measures of morbidity in 107 consecutively delivered obese women undergoing cesarean. Although obesity is clearly an operative risk factor, this study suggested that among obese gravidas, varying degrees of maternal obesity and accompanying medical complications, such as diabetes and hypertension, were not associated with greater operative morbidity. Furthermore, neither choice of skin incision nor type of anesthesia appeared to be related to operative morbidity. However, two factors potentially under the control of the clinician, increased length of surgery and operative blood loss, were associated significantly with measures of operative morbidity. A finding of worsened outcome with prophylactic antibiotics and heparin requires further study.