In the past 5 years at our institution, 12 cases involving the ingestion of chlorpropamide 3-15 g were fatal. We report a 23-year-old woman with an estimated ingestion of chlorpropamide 5-10 g. Initial cardiovascular collapse, attributed to the blockade of potassium channel transport, responded to intensive support including 3 days of cardiac pacing. Urinary excretion of chlorpropamide and hypoglycemia persisted until day 27. The toxic mechanisms and high risk of chlorpropamide are summarized. A fatal therapeutic dose ratio as low as 4:1 has made this antidiabetic agent obsolete.