One newborn child was selected from 14 families in which kwashiorkor had occurred. Undernutrition in this test group was prevented for the first two years of life by the provision of supplementary feeding. Controls who were the siblings directly preceding each of the 14 test children received no supplementary feeding, but received medical attention and management. In each family an older child who previously had kwashiorkor (kwashiorkor group), and the nearest sibling who had received neither extra feeding nor medical management (kwashiorkor control group) were also available for comparison. A battery of psychologic tests was administered when the mean age of the test group was 8.9 years. The mean fullscale IQ of the supplementary feeding group at an average age of 8.9 years was significantly higher than that of any of the other three groups. There was no significant difference between test and control groups on nonverbal IQ. Measures of "brain damage" did not discriminate between any of the four groups. The results suggest that nutritional factors contribute especially to the elevation of verbal intelligence. Environmental stimulation (daily contact with a more alert child) apparently contributed to the elevation of the nonverbal scores of the controls. © 1980 The C. V. Mosby Company.