Objective. We sought to examine perinatal outcomes in women with a body mass index (BMI) of 25 kg/m 2 comparing those whose weight gain met 2009 IOM guidelines to women meeting 1990 IOM guidelines. Methods. This is a retrospective cohort study utilizing birth records linked to hospital discharge data for all term, singleton infants born to overweight, Missouri residents (2000-2006) with a BMI of 25 kg/m 2. We excluded congenital anomalies, mothers with diabetes, hypertension, or previous cesarean delivery. Results. Fourteen thousand nine hundred fifty-five women gained 25-35 lbs (1990 guidelines); 1.6% delivered low birth weight (LBW) infants and 1.1% delivered macrosomic infants. Eight thousand three hundred fifty women gained 15-25 lbs (2009 guidelines); 3.4% delivered LBW infants and 0.6% delivered macrosomic infants. Women who gained 15-25 lbs were 1.99 (95% CI 1.67, 2.38) times more likely to have a LBW infant and 0.59 (95% CI 0.40, 0.76) times less likely to deliver a macrosomic infant. Conclusion. Limiting weight gain in women with a BMI of 25 kg/m 2, per the 2009 guidelines, increases the risk of LBW deliveries and decreases the risk of macrosomia but does not reduce associated adverse perinatal outcomes. Further studies should explore the optimal weight gain to reduce these outcomes. © 2011 Informa UK, Ltd.