OBJECTIVE To determine whether the postnatal growth rate of infants with intrauterine growth restriction (IUGR) is associated with later cognitive function and body mass index (BMI). METHODS Infants with IUGR (<2211 g at > or =37 weeks' gestation) were identified in data from the Collaborative Perinatal Project, excluding those with diagnoses affecting cognition or growth. Wechsler Scale of Children's Intelligence (WISC) scores at age 7 years and data on postnatal growth at 16 weeks were available for 463 infants with IUGR. Linear regression relating postnatal growth and WISC score, adjusting for potential confounders, was performed for these infants. BMI at 7 years also was examined. RESULTS Weight gain at 16 postnatal weeks ranged from 1059 to 5119 g in the infants with IUGR, with lower achieved cognitive testing scores apparent at both extremes (ie, an inverted J-shape; P < .001). Infants gaining 1200 and 5000 g scored 15.5 and 2.4 fewer points, respectively, on the full scale compared with infants with score-maximizing growth. In contrast, BMI at 7 years was linearly related to postnatal weight gain (P < .001). CONCLUSIONS Growth in the first 4 postnatal months is an independent risk factor for cognitive outcome at age 7 years, with both extremes associated with negative effects.