We investigated whether obese infants tend to become obese adults. Records of subjects born between 1945 and 1955 were reviewed to select three cohorts based on weight in the first six months of age, which exceeded the 90th percentile at least once, ranged between 25th and 75th percentiles or was below 10th percentile at least once. Three hundred and sixty-six subjects, now between 20 and 30 years of age, were located and their present height and weight determined. Thirty-six per cent of those exceeding the 90th percentile as infants were overweight adults, as compared to 14 per cent of the average age and light-weight infants. A significant increase (chi square = 17.2, p less than 0.001) in adult obesity was evident when the infant exceeded the 75th percentile that was independent of his height. Social class, educational level, and parental weight all correlated with adult weight (p less than 0.001). Sex and ordinal position of birth did not. The data suggest that infant weight correlates strongly with adult weight independently of other factors considered.