The etiology of transient global amnesia is poorly understood, particularly in children and young adults. Transient global amnesia may follow a wide range of precipitating events. Proposed causes have included vascular event, seizure, and migraine. A young man with cyanotic congenital heart disease experienced an episode of transient global amnesia in the setting of polycythemia. Differential diagnosis of acute confusional episodes in children should include transient global amnesia, as well as confusional migraine, and should include evaluation for underlying coagulation abnormalities and polycythemia.