A study group of 795 women was followed with frequent weight measurements and questionnaires about their activities for 6 months postpartum. The mean (± SD) net weight gain from the first prenatal visit to 6 months postpartum was 1.4 ± 4.8 kg. Weight gain during prenatal care was the variable most highly correlated to weight loss. Return to work outside the home, parity, and smoking also correlated significantly to weight loss. Breast-feeding, exercise, season of the year, age, and marital status were not correlated. Route of delivery was related to weight loss at 2 and 6 weeks, but not at 6 months. Counseling women about weight gain during pregnancy and weight loss requires an understanding of these variables with a long-term perspective of at least 6 months.(Obstet Gynecol 1992;79:424-9)