Maternal pregravid obesity is a significant risk factor for adverse outcomes during pregnancy. In early pregnancy there is an increased risk of spontaneous abortion and congenital anomalies. In later gestation maternal metabolic manifestations of the metabolic syndrome, such as gestational hypertensive disorders and diabetes, become clinically recognized because of the increased insulin resistance in obese compared with nonobese women. In women with pregestational glucose intolerance, hypertension, central obesity, and lipid disorders, the physiologic changes in pregnancy increase the risk of problems previously not routinely encountered during pregnancy. These include chronic cardiac dysfunction, proteinuria, sleep apnea, and nonalcoholic fatty liver disease. At parturition the obese patient is at an increased risk of cesarean delivery and associated complications of anesthesia, wound disruption, infection, and deep venous thrombophlebitis. For the fetus there are short-term risks of fetal macrosomia, more specifically obesity, and long-term risks of adolescent components of the metabolic syndrome. Although preliminary results of bariatric surgery are encouraging, the procedure is expensive and not for all obese women, and we recognize that long-term follow-up data on offspring of obese women who have undergone bariatric surgery before pregnancy are lacking. In the interim, we need to encourage obese women to lose weight before conception, using lifestyle changes if possible. During pregnancy, weight gain should be limited to Institute of Medicine guidelines (currently under review) and encouragement given for physical activity.