BACKGROUND: The postpartum period may be critical for the development of midlife obesity. Identifying factors associated with postpartum weight change could aid in targeting women for healthy lifestyle interventions. METHODS: Data from Active Mothers Postpartum (AMP), a study of overweight and obese postpartum women (n=450), were analyzed to determine the effect of baseline characteristics, breastfeeding, diet, physical activity, and contraception on weight change from 6 weeks to 12, 18, and 24 months postpartum. The repeated measures mixed model was used to test the association of these effects with weight change. RESULTS: Although mean weight loss was modest (0.49 kg by 24 months), the range of weight change was striking (+21.5 kg to -24.5 kg, standard deviation [SD] 7.4). Controlling only for baseline weight, weight loss was associated with breastfeeding, hormonal contraception, lower junk food and greater healthy food intake, and greater physical activity. Only junk food intake and physical activity were significant after controlling for all other predictors. CONCLUSIONS: Eating less healthy foods and being less physically active put overweight and obese women at risk of gaining more weight after a pregnancy.