BACKGROUND: More than 40% of women with a normal pre-pregnancy body mass index (BMI) exceed the 2009 Institute of Medicine (IOM) guidelines' recommended weight gain of 25-35 lb. Excessive gestational weight gain is one modifiable factor that may be contributing to childhood overweight and obesity. OBJECTIVE: The objective of this study was to evaluate differences in adiposity from neonates born to mothers with a normal pre-pregnancy BMI who either gained within or above IOM guidelines. METHODS: Neonatal adiposity was measured within 72 h of birth by the method of air displacement plethysmography. RESULTS: Compared with mothers who gained within IOM guidelines (N = 27), mothers with excessive gestational weight gain (N = 11) (mean 29.0 vs. 45.2 lb) had neonates with 50% more fat mass (348 vs. 525 g) and 3% greater body fat (10.7 vs. 13.9%). CONCLUSIONS: Increased adiposity at birth may predispose these children to increased risk of obesity and highlight the importance that women avoid gaining excessive weight in pregnancy.