In the period 1968-1989 50 patients, 38 women and 12 men, aged 30-76 years, median 58 years, were referred to the Department of Gastroenterology, Rigshospitalet for severe chronic radiation enteropathy. Most women had received radiation for gynaecological cancer, and most men for urogenital cancer. The initial symptoms of the enteropathy were diarrhoea in 74%, abdominal pain in 62% and weight loss in 52%. Twelve per cent had visible blood in the stools. Ten per cent had fistulas. The symptoms occurred 0-37 years, median ten months after the radiation. The radiation enteropathy had necessitated one or more laparotomies in 35 patients, most often because of subileus/ileus, including resection of the small bowel or the colon in 25 patients, and establishment of an ileostomy or a colostomy in 11. Seven patients developed new fistulas postoperatively. In 32 patients one or more tests for malabsorption were performed as a guidance for therapy: stool mass (26 patients), faecal fat excretion (26 patients), Schilling test (22 patients), lactose absorption (11 patients) and bile acid breath test (seven patients). Half of the patients had diarrhoea, including one third of the patients without intestinal resection. Two thirds had steatorrhoea, including half of the patients without small bowel resection. Three fourths showed decreased absorption of vitamin B12, including half of the patients without ileal resection. All patients studied had abnormal deconjugation of bile acids and more than half of them had bile acid malabsorption. Malabsorption of lactose was found in only one patient. There was no correlation between the radiological and functional abnormalities of the small intestine.(ABSTRACT TRUNCATED AT 250 WORDS)