OBJECTIVE To determine if postnatal growth failure exerts an adverse effect on subsequent growth and neurodevelopment. METHODS A secondary analysis of 1018 infants who were enrolled in a randomized, clinical trial of glutamine supplementation was performed to determine whether early provision of parenteral amino acids (AA) is associated with better growth and neurodevelopmental outcomes. Infants were stratified by whether they were provided > or =3 g/kg per day of AA at < or =5 days of life (early; n = 182) or not (late; n = 836). RESULTS At 36 weeks' postmenstrual age, significant differences were found in weight, length, and head circumference in favor of the infants who received early AA; the odds of having weight less than the 10(th) percentile for age was 4-fold higher for infants in the late group. At 18 months' CA, there were no differences in weight, length, or measures of neurodevelopment between the groups; however, male infants in the late group were twice as likely to have head circumference less than the 10(th) percentile. CONCLUSIONS Early AA were associated with significantly better growth outcomes at 36 weeks' postmenstrual age, and fewer infants who received early AA were found to have suboptimal head growth at 18 months' CA.