Chronically ill children often become malnourished. These children have increased metabolic requirements and increased losses associated with impaired absorption and decreased nutrient usage. In hospitalized children nutritional assessment is rarely performed, increased or modified needs are not recognized, meals are omitted due to analysis or interventions, which lead to a further decline in nutritional status. The consequences of malnutrition are growth retardation and slow development, aggravation of a disease, impaired immunity and decreased resistance to infection. Nutritional support should improve the quality of life in chronically ill children. Adequate nutritional support should provide that the growth of these children corresponds to the growth of the healthy children of the same age group. The course of disease could be improved too. The enteral route of feeding is the best choice, so enteral nutrition (EN) should be the first option, but in the occasions when it is contraindicated parenteral nutrition (PN) is applied. This review article discusses cardiac, renal and liver diseases, cystic fibrosis and AIDS in children, from the nutritional point of view.