SummaryThe histories of 6 cases, 2 male and 4 female, with glucose‐galactose malabsorption (GGM) are presented. Of these, 4 have survived and are in good general health on a diet with a reduced carbohydrate content. One case died at 2 months of age with severe malnutrition due to intractible diarrhoea before a diagnosis was made. The other patient who died, was diagnosed and treated from the neonatal period, and he was progressing until infection occurred by aCandida albicans, followed by death at 3 months of age in a picture of agam‐maglobulinaemia. One patient is now a woman of 41. The main symptoms are diarrhoea from birth, dehydration and malnutrition. Glucose is found in the watery stools and there is also a slight glucosuria. Hyperosmolar serum is often seen. Two patients, not those treated at an early stage, developed renal concrements probably owing to the long lasting water loss with the stools. Treatment during the first months consisted of replacement of the ordinary dietary carbohydrates by fructose. Although the basic biochemical disorder lasts throughout life, limited amounts of starch and milk could be introduced later in infancy. Some absorption of glucose could be demonstrated, tentatively due to a second pathway for intestinal glucose absorption which is apparently not shared by galactose. Hydrolysis of disac‐charides occurred in the small intestine of GGM patients but the released glucose was absorbed no better than when administered as a monosaccharide. This implies that the site of disaccharidase activity is located more superficially at the luminal side of the epithelial cell membrane than the disturbed step of glucose and galactose tran