We present a case of a 22-year-old man who died unexpectedly after a seizure due to a previously undiagnosed calcifying pseudoneoplasm of the neuraxis (CAPNON). Calcifying pseudoneoplasm of the neuraxis is a rare entity, and this is, to our knowledge, the first described case of sudden death due to CAPNON. Sudden death due to undiagnosed central nervous system mass lesions is rare, and most cases are attributable to hemorrhage, hydrocephalus, or increased intracranial pressure due to mass effect. Seizure is a rare cause of sudden death due to central nervous system mass lesions. This case highlights that mass lesions may cause sudden death due to seizure, even without other pathologic evidence of a cause of death, such as hemorrhage or edema. Furthermore, benign, reactive, and low-grade mass lesions may cause sudden death due to seizure. Seizure should remain in the autopsy differential as a cause of death, even where there is no pathologically evident mechanism by which a mass lesion caused death.