A population-based cohort of 1458 Brazilian infants was followed from birth to 9-15 months of age to investigate the effects of birthweight and family income on subsequent growth. There was a strong association between birthweight and attained weight and length, while virtually no malnutrition among children who weighed more than 3000 g at birth; Children with lower birthweights tended to put on less weight during the first year, but these differences were no longer significant after controlling for family income. As a result, infants of lower birthweights tended to remain behind those of higher birthweights. Children from the wealthiest families gained 20% more weight than low-income infants, irrespective of birthweight. Low birthweight infants from high-income families were therefore likely to approach the standard weight at one year old while those from poor families lagged behind.