In pediatrics, oral rehydration treatment is increasingly used in the management of gastroenteritis, and based on third world experiences, it is becoming used also in hospitals in western countries. In this paper, the advantages, limitations and practical use of oral rehydration treatment are discussed. Clinical examination of dehydrated children is described, and guidelines are given for intravenous fluid treatment. Furthermore, the article reviews modern research on the nutritional management of gastroenteritis. The incidence of secondary lactose intolerance has been dramatically reduced in recent decades, and this necessitates some changes in our traditional nutritional therapy. Rest of the bowels, and removal of lactose from the diet are seldom justified.