A study of maternal glucose tolerance conducted during 137 pregnancies in which the infant weighed 4540 g or more at birth revealed an increased incidence of hyperglycemia (20.4%, P < 0.01). Only when a birth weight of more than the 99th percentile was considered was a significant association with maternal hyperglycemia evident. However, 105 of the 137 patients (77%) had normal glucose tolerance, which indicated that hyperglycemia is not necessarily the cause of fetal overgrowth. When a woman delivers an infant with a birth weight of 4540 g or more, it cannot be assumed that she was a gestational diabetic.