The Stockholm Pregnancy and Weight Development Study is a prospective study of body weight changes in women, whose maternity unit charts were reviewed and who were then invited for a 1-year follow-up, including weigh-in sessions and questionnaires on dietary habits, physical activity and socio-demographic factors. Total weight gain during pregnancy was related to weight gain already during the first trimester. Women reporting previous weight cycling had slightly higher weight gain during pregnancy. Successful return towards pre-pregnancy weight was found more often in women with regular breakfast and lunch habits. Lactation had only a small effect on weight loss after delivery, independent of eating habits. Lack of physical activity was more common in women who had low lactation scores. Twenty-eight percent reported an increased interest in sweets during pregnancy; these women increased 1 to 2 kg more than others in weight during pregnancy. Postpartum weight retention was more affected by lifestyle changes during and after pregnancy than by factors before pregnancy.