Most cancers in children are acute diseases. Therefore, the incidence of malnutrition, in general, is not different from the incidence in the referral population. Some specific tumors, such as neuroblastoma and those resulting in the diencephalic syndrome, can be exceptions. By contrast, malnutrition is a frequent problem during modern intensive cancer treatment as the result of the associated anorexia, altered taste sensations and catabolic effects of drugs. In addition, there are psychogenic factors and metabolic consequences associated with the tumor itself. Nutritional support does improve the feeling of well-being and performance status, while maintaining or improving the immune competence, thereby potentially affecting survival by limiting infectious episodes. There is no convincing evidence to date that nutritional support has an antineoplastic effect per se, but deficiency of a specific nutrient might be beneficial because of a differential requirement between tumor and normal cells. Theoretically, nutritional support might enhance tumor growth but also susceptibility to chemotherapy. In either case, nutrition is a support modality that must be given with appropriate tumor-directed therapy if curative intent is the goal of treatment. Nutrition remains a consideration after therapy is completed. This generates different challenges. If further tumor-directed therapy is futile, the decision to continue nutritional support is difficult, but if the child is well, nutritional rehabilitation must be pursued. Finally, the cured child continues to benefit from dietary advice. Nutrition should be viewed for what it is: supplying the most basic need of children.