A case of recurrent hypoglycemic coma precipitated by tolazamide (Tolinase) at therapeutic dosage is here reported. The patient, an elderly woman with diabetes and renal failure, experienced several episodes of profound hypoglycemic coma, the last one forty-eight hours after withdrawal of the sulfonylurea. With this report, cases of prolonged hypoglycemia have been described with all currently available hypoglycemic sulfonylureas.