Antiarrhythmic-induced hypoglycemia is an ill-defined phenomenon. Sporadic cases have been reported with disopyramide, a class IA antiarrhythmic agent. We report a case of cibenzoline-induced hypoglycemia in an elderly male with a history of ischemic heart disease, congestive heart failure, ventricular arrhythmias, and chronic obstructive pulmonary disease. Cibenzoline is a class I antiarrhythmic agent currently undergoing clinical investigation in the U.S. The initial hypoglycemic episode occurred after two years of successful treatment with cibenzoline. Blood glucose during the first hypoglycemic episode was 40 mg/dL. The hypoglycemia was associated with central nervous system depression, hyperkalemia, electrocardiographic abnormalities, and respiratory distress. Rechallenge with cibenzoline resulted in recurrence of symptoms and a blood glucose level of 21 mg/dL. A second rechallenge resulted in symptoms suggestive of hypoglycemia, but cibenzoline was discontinued before frank hypoglycemia and hyperkalemia recurred. Hypoglycemia occurred during periods of fasting, which most likely ruled out reactive-type hypoglycemia. Insulinoma was ruled out by the presence of normal fasting blood glucose and plasma insulin levels. It was concluded that this patient's hypoglycemia was secondary to cibenzoline. Hypoglycemia is a rare and sporadic adverse effect associated with antiarrhythmic therapy. However, the severity of these reactions warrants increased awareness of their occurrence in patients presenting with symptoms of hypoglycemia who are receiving disopyramide or cibenzoline.