We examined the risk of maternal obesity in 588 pregnant women weighing at least 113.6 kilograms (250 pounds) during pregnancy. Compared with a control group matched for age and parity, we found a significantly increased risk in the obese patient for gestational diabetes, hypertension, therapeutic induction, prolonged second stage of labor, oxytocin stimulation of labor, shoulder dystocia, infants weighing more than 4,000 grams and delivery after 42 weeks gestation. Certain operative complications were also more common in obese women undergoing cesarean section including estimated blood loss of more than 1,000 milliliters, operating time of more than two hours and wound infection postoperatively. These differences remained significant after controlling for appropriate confounding variables. We conclude that maternal obesity should be considered a high risk factor.