163 patients were admitted to the Cantonal Hospital, Basel, during the decade 1968--1978 with severe diabetic ketoacidosis or non-ketotic coma. The hospital mortality rate was 28% in the first period (1968--1973) but decreased to 14% (p less than 0.025) in the second period (1973--1978). The lower mortality rate in the second period was due to diminished early mortality within 3 days after admission. The decline in the mortality rate during the second period was assumed to be due to a general improvement of treatment and possibly to a direct effect of low-dose insulin therapy. The latter conclusion followed from the fact that the remaining recompensation therapy, such as fluid and electrolyte replacement, was similar during both periods. However, in the non-ketotic patients low-dose insulin therapy resulted in a delayed fall in blood glucose and distinctly diminished potassium retention. The fatalities in the second period of treatment were mainly due to thromboembolic complications. This points to the need for a search for preventive measures against thromboembolism in order to resuce mortality in severe diabetic coma further.