Between 1969 and 1976, 317 adults were admitted to hospital in Nottingham with severely uncontrolled diabetes (plasma glucose over 33 mmol/l and/or venous bicarbonate less than 14 mmol/l). A third of episodes were in patients over the age of 50 years, of which 43% were fatal. In contrast, only 3.4% of episodes in patients under 50 years were fatal. In the older group, 65% of deaths occurred within 48 h of admission and in 44% no cause was found other than uncontrolled diabetes. Later deaths were due to underlying disease, infection or thromboembolism. Amongst older patients 38% were not previously known to have diabetes. Presentation to hospital was late and we conclude that many deaths were potentially avoidable by earlier detection in the community.