Thirty-one children with sucrose malabsorption are reported. All had a flat blood sugar curve after sucrose ingestion but a normal one after monosaccharides. Seventy-five percent were malnourished and 11 were dehydrated at admission to hospital. Seven had to have intravenous rehydration. After institution of a sucrose-free diet, the symptoms disappeared and the patients gained weight. Eighteen had had symptoms for greater than 1 year, 13 for greater than 2 years, and 7 for greater than 5 years before their cause was discovered. Familial occurrence of sucrose malabsorption was shown in three to five cases. Four children were reinvestigated 7-15 years after diagnosis. All had chronic dyspepsia, and none kept a strictly sucrose-free diet. Three of the four patients were underweight for their age by from 5 to 16 kg, whereas the fourth was as underweight as compared to height. It is concluded that the high incidence of sucrose malabsorption found in Greenland together with the high sucrose consumption might be of nutritional hygienic significance for the population.