Postnatal growth failure is extremely common in the very low birth weight and extremely low birth weight infant. Recent data from the National Institute of Child and Human Development (NICHD) Neonatal Research Network indicates that 16% of extremely low birth weight infants are small for gestational age at birth, but by 36 weeks corrected age, 89% have growth failure. Follow-up at 18 to 22 months corrected age shows that 40% still have weights, lengths, and head circumferences less than the 10th percentile. Growth failure is associated with an increased risk of poor neurodevelopmental outcome. Inadequate postnatal nutrition is an important factor contributing to growth failure, as most extremely low birth weight infants experience major protein and energy deficits during the neonatal intensive care unit hospitalization, in spite of the fact that nutrition sufficient to support intrauterine growth rates can generally be provided safely. Aggressive nutritional support--parenteral and enteral--is well tolerated in the extremely low birth weight infant and is effective in improving growth. Continued provision of appropriate nutrition (premature formula or fortified human milk) is important throughout the neonatal intensive care unit stay. After discharge, nutrient-enriched postdischarge formula should be continued for approximately 9 months post-term. Exclusively breast-fed infants require additional supplementation/fortification postdischarge as well. Additional trials are needed to address a number of important questions concerning the role of nutrition and growth on ultimate development.