From 1980 to 1985, 120 insulin-dependent diabetics were admitted to the emergency department of the Cantonal Hospital, Basle, for altogether 173 severe hypoglycemic attacks. Relating these numbers to a total of 700 insulin-dependent diabetics in Basle, this means an hypoglycemia incidence of 4.2 per 100 treatment years. The principal causes were: dietary error or increased physical activity ... [Show full abstract] (43.7%); increase in daily insulin dose by the patient or his doctor (14.6%); and other illnesses, mostly involving the gastrointestinal tract (10.9%). Age and duration of insulin treatment were risk factors for the occurrence of hypoglycemic episodes. Thus, comparing patients at the Cantonal Hospital with or without hypoglycemia, there were significantly more hypoglycemic attacks (p less than 0.05) in the group of patients aged over 60 years or who had been treated with insulin for more than ten years. Average daily dose of insulin was about the same in both groups (35.8 U daily with hypoglycemia; 39.6 U without). Regardless of the daily number of injections, hypoglycemia occurred most frequently between 10 and 13 h and before the evening meal between 17 and 19 h.