Prevalences of underweight for age in South African schoolchildren rose from seven years to reach high levels during puberty. In Black children at the height of the pubertal growth spurt, half to three-quarters were underweight for age and hence classifiable as "malnourished". However, percentages fell rapidly to one-fifth or less at 17 years. High prevalences of stunting were common in Blacks. Wasting occurred in similar proportions of urban Black compared with White children, i.e., the large majority of both Blacks and Whites were normally proportioned; younger children were more wasted than older pupils. Factors additional to nutrition appear to share in the regulation of growth. In Whites on adequate diets, there were (i) similar patterns, but smaller rises in underweight prevalences over the growth spurt, also (ii) small but not insignificant prevalences of stunting: (iii) closely similar "normal" patterns of weight for height occurred in Whites as well as Blacks, and (iv) in Blacks the sharp fall in prevalences of underweight and wasting, after the rapid growth phase, occurred without any dietary intervention. A plea is made to use not only weight, but height, particularly relative to weight, at all ages, in assessing nutritional status and "at risk" groups. The stunted and wasted child is likely to be at greater risk than a similarly stunted but normally proportioned or overweight child--both could be underweight for age. Further definitive studies are required.