Reports by the Institute of Medicine (IOM) recommend that gestational weight gain goals should be modified according to prepregnancy body mass index (BMI), which could result in better maternal and infant outcomes. The authors assessed whether the risk of the pregnancy outcomes such as rate of cesarean section to primiparous and multiparous women, macrosomia, and breastfeeding at 10 weeks postpartum can be modified by following the IOM guidelines for gestational weight gain irrespective of prepregnancy BMI. Staff from the New Jersey Pregnancy Risk Assessment Monitoring System interviewed a sample of women who delivered live births in New Jersey during 2002 through 2005 (n = 7661). In New Jersey, 18% of mothers were obese, 13% were overweight, and 16% were underweight. In logistic regression analyses, after controlling for maternal characteristics, the effect of prepregnancy obesity and weight gain more than 34 lb independently and significantly increased the risk of all four adverse outcomes. For no outcomes was the 25- to 34-pound weight gain category significantly distinguishable from the 16- to 24-pound reference category. These results strongly support the idea that the IOM weight gain recommendation (education during preconception regarding the importance of optimal BMI at the start of pregnancy) will help to achieve better pregnancy outcomes in obese and overweight women.