During a 12-month prospective study there were 125 visits to the Harlem Hospital Emergency Room for symptomatic hypoglycemia. Sixty-five patients had obtundation, stupor, or coma; 38 had confusion or bizarre behavior; 10 were dizzy or tremulous; 9 had had seizures; and 3 had suffered sudden hemiparesis. Diabetes mellitus, alcoholism, and sepsis, alone or in combination, accounted for 90% of predisposing conditions; others included fasting, terminal cancer, gastroenteritis, insulin abuse, and myxedema. Average blood glucose levels were lower among comatose than among obtunded patients, but overlap was considerable, and overall there was little correlation among cause, blood glucose levels, and symptoms. Although mortality was 11%, only one death was attributable to hypoglycemia per se, and only four survivors had focal neurological residua.