We report 2 cases of sudden death in which hospital autopsies revealed unsuspected primary posterior fossa neoplasms. The first case was a 3-year-old girl who was found apneic and pulseless in bed and was brought to the hospital moribund and could not be resuscitated. Autopsy revealed a 3-cm ganglioglioma that infiltrated nearly the entire medulla. The second case involved a 39-year-old man who was found asystolic and unresponsive in bed. He was resuscitated and maintained on a ventilator for a few hours, after which life support was withdrawn. Autopsy showed a 5-cm pilocytic astrocytoma arising from the ventral cerebellum and extending into the fourth ventricle and compressing the brain stem. Previously reported cases of clinically unsuspected primary posterior fossa tumors presenting with sudden death are reviewed. Hypotheses for the mechanism of sudden death are presented.