The growth patterns of 158 infants with significant intrauterine growth retardation (IUGR) were studied for the first 2 years of life. Eighty-four infants were born after 36 completed weeks. All these full-term infants survived; complete follow-up data were obtained for 78. Acceleration of growth in weight began soon after birth and continued for an average of 6 months. Acceleration of linear growth began somewhat later, but was limited to the first 9 months. Twenty-three infants (29%) were still below the 5th centile for both weight and height by 2 years of age. There was a negative correlation between the neonatal ponderal index and length at 18 months for females only. Seventy-four infants were born prematurely, before 37 weeks' gestation. Mortality in this group was 18% and complete follow-up data were obtained for 49 of the 61 survivors. Birth weight was regained on average at 11 days; accelerated weight velocity began 4-6 weeks before the expected date of delivery (term date). The potential for catch-up growth lasted up to 9 months after the term date. By 18 months, however, 44% of these pre-term infants were still below the 5th centile for weight. Size at 18 months post-term was correlated with weight at the term date and length at 3 months post-term, but not with the degree of IUGR or with the ponderal index.