Two cases of sudden death due to colloid cysts of the third ventricle are presented with a review of the literature. In the first case, a 40-year-old woman suffered an acute onset of severe frontal headache after an intercontinental air flight. The next day, she was found comatous and died 7 h after admission to a hospital. In the second case, a 33-year-old man with a medical history of recurrent headaches was found dead in his car. Autopsy in both cases revealed a colloid cyst of the third ventricle and hydrocephalus involving the lateral ventricles. These cases demonstrate that fatal cases still occur. Nevertheless, prompt diagnosis using computed tomography (CT) or magnetic resonance imaging (MRI) is essential, since colloid cysts are histologically benign tumors that can be removed safely by neurosurgical intervention.