The records of 517 pregnancies which terminated in the delivery of infants weighing 9 lb or more were reviewed. The obstetric patient most likely to deliver a large birth weight infant was characterized. Toxemia, prolonged labor, and puerperal morbidity occurred with increased frequency. Many of the deliveries were complicated by fetopelvic disproportion with resultant increase in mid forceps deliveries, cesarean sections, and perinatal morbidity. Five of the 517 patients delivering large birth weight infants were known to have diabetes mellitus prior to le pregnancy included in this study. An additional 369 patients were evaluated with intravenous glucose tolerance tests. Thirty-eight (10.3%) of the 369 tested proved to lave diabetic glucose tolerance curves. The likelihood of [hiding maternal diabetes mellitus increased with the infant's birth weight. Multiple regression analysis of other clinical variables failed to predict which patients would prove to have diabetes. Identification of diabetic puerperas requires that glucose tolerance tests be performed in all who deliver large birthweight infants.