The most liberal published guidelines for maternal weight gain at term suggest a range of 9-14 kg. In a cohort of 4674 women with good pregnancy outcomes who delivered at the University of California, San Francisco between 1980-1988, the lower end of the currently published weight gain range was relevant, but the upper limit of weight gain was higher. Good pregnancy outcome was defined as a vaginal birth between 37-42 weeks' gestation of a living, singleton infant of appropriate birth weight for gestational age without congenital anomalies, born to a mother who did not experience diabetes or hypertension during pregnancy. Ranges of 12-18 and 10-21 kg described 50 and 80% of the group, respectively. Mean weight gain was associated with maternal pre-pregnancy body mass, parity, and race, with the largest differences observed in overweight and obese women. The results reported here suggest that a wider range of maternal weight gain than is currently recommended is associated with good pregnancy outcome.