To investigate maternal body weight development after pregnancy and to determine the effect of pregravid nutritional status and gestational weight gain on weight change. Design. Prospective cohort study.The population under study consisted of 486 women aged 16-41. Maternal body mass index (BMI) was calculated using the reported pregravid weight, and was stratified into four categories: underweight (less than 19.8), normal weight (19.8 to 26.0), overweight (26.1 to 29.0), and obesity (more than 29.0). Body weight was measured at 3,6, and 12 month after delivery. Gestational weight gain was stratified into quartiles for this patient population.The mean weight gain after 1 year post-partum compared with the prepregnancy body weight was 1.0 +/- 3.6 kg. Of the group 36.5% lost weight, 53.7% gained 0-5 kg, 8.0% gained 5-10 kg and 1.8% gained > 10 kg. Obese women tended to retain more weight after pregnancy -2.4 +/- 3.7 kg, than lighter women -0.8 +/- 3.2 kg (non-significant). Women who had a pregnancy weight gain in the highest quartile (> 16.5 kg) had a mean weight gain of 1.8 +/- 3.9 kg, while women in the lowest quartile (< or = 11 kg) -0.3 +/- 3.4 kg (p < 0.001).Pregnancy is a risk factor for postpartum weight retention, although distribution (%) of weight change showed large scatter of results. The factors contributing to postpartum weight changes are prepregnancy body weight and prenatal weight gain.