Dieulafoy's lesion is an abnormal submucosal artery in the stomach characterized by massive and often fatal upper gastrointestinal hemorrhage. Diagnosis is usually made at operation, as endoscopy and arteriography frequently fail to identify the lesion. Embolization may be helpful, but surgery is generally the treatment of choice. We present the first reported case of Dieulafoy's lesion in a 17-yr-old boy with type IV truncus arteriosus. This congenital cardiac anomaly may have predisposed this patient to early manifestation of Dieulafoy's lesion, a rare and frequently unrecognized disorder.