To examine the relative importance of intrauterine growth failure, extrauterine growth failure before or after term, and the prognostic significance of catch-up growth, 192 very low--birth weight infants (less than 1.5 kg) were followed prospectively to 8 months corrected age. One hundred fifty-four appropriate--for--gestational age (AGA) and 38 small--for--gestational age (SGA) infants were categorized into normal and subnormal (less than -2 SD) weight for age groups at term (40 weeks) and at 8 months corrected age. By term, 71 AGA infants had subnormal weight; 41 of these caught up by 8 months, and an additional 13 AGA infants failed to thrive between term and 8 months. Of the SGA infants, three caught up in weight by term, and an additional 16 caught up by 8 months. Significant correlates of subnormal weight included neonatal risk score, incidence of chronic disease, and extended hospitalization. The AGA and SGA infants who failed to thrive or failed to catch up in weight by 8 months had lower mean Bayley developmental quotients (p less than 0.005), smaller head circumferences (p less than 0.005), and a higher rate of neurosensory impairment (p less than 0.01) than the AGA infants with normal fetal and postnatal growth. Intrauterine and/or postnatal growth failure prior to term was not of sinister prognostic significance if catch up occurred thereafter.