Sulfonylureas are the most frequently used peroral antidiabetic drugs in Norway. Five cases of serious sulfonylurea-induced hypoglycemia are described. In one of these cases glibenklamid-induced hypoglycemia was thought to be the direct cause of death. A review of the literature indicates that glibenclamide induces more frequent and serious hypoglycemias than other sulfonylureas do. The author discusses the possible mechanisms behind these differences, and the conditions predisposing to sulfonylurea-induced hypoglycemia. It is recommended to check blood glucose whenever a patient's diagnosis has not been adequately clarified.