Objective To explore risk factors for postpartum weight retention at one year after delivery in predominantly low income women. Methods Data were collected from 774 women with complete height and weight information from participants in the NICHD Community Child Health Network, a national five-site, prospective cohort study. Participants were enrolled primarily in the hospitals immediately after delivery. Maternal interviews conducted at 1, 6, and 12 months postpartum identified risk factors for weight retention and included direct measurement of height and weight at 6 and 12 months. Logistic regression assessed the independent contribution of postpartum weight retention on obesity. Results Women had a mean prepregnancy weight of 161.5 lbs (BMI 27.7kg/m2). Women gained a mean of 32 lbs while pregnant and had a 1 year mean postpartum weight of 172.6 lbs (BMI 29.4kg/m2). Approximately 75% of women were heavier 1 year postpartum than they were prepregnancy, including 47.4% retaining over 10 lbs and 24.2% over 20 lbs. Women retaining at least 20 lbs were more often African American, younger, poor, less educated, or on pubic insurance. Race and socioeconomic disparities were associated with high pre-pregnancy BMI and excessive weight gain during pregnancy, associations which were attenuated by breastfeeding at 6 months and moderate exercise. Of the 39.8 with normal prepregnancy BMI, one third became overweight or obese 1 year postpartum. Conclusion Postpartum weight retention is a significant contributor to the risk for obesity 1 year postpartum, including for women of normal weight prepregnancy. Postpartum, potentially modifiable behaviors may lower the risk.