Abnormal growth is a common feature of thalassaemia major in children. In an attempt to determine whether it has a nutritional cause, 12 children aged 1 to 3 years with thalassaemia major were studied under metabolic ward conditions. Nutritional status was assessed by anthropometry and biochemistry before and after an intensive nutrition regimen. Five children had wasting or stunting on admission. As a result of the nutrition intervention, mean weight for height improved significantly. The mean height increase of 0.4 cm after one month was not significant. Plasma zinc, depressed in half the children on admission, improved, as did alpha tocopherol, while copper decreased. Plasma insulin-like growth factor-I also increased commensurate with improved growth. Fat absorption was normal in all children. Undernutrition is an important cause of associated growth disturbances in children with thalassaemia major. Malnutrition was primarily caused by inadequate nutrient intake, as indicated by the capacity to gain weight appropriately when provided with nutrition support, and by the absence of intestinal malabsorption. While long term studies are required to determine if nutritional support will prevent stunting, these results underscore its central role in preventing nutritional deficiencies and in promoting normal growth in thalassaemic children.