Sudden unexpected death in epilepsy is the most common category of seizure-related death in patients who develop chronic epilepsy, accounting for up to 17% of epilepsy deaths. Sudden unexpected death in epilepsy is defined as a sudden, unexpected, non-accidental death in an individual with epilepsy with or without evidence of a seizure having occurred (excluding documented status epilepticus) and where autopsy does not reveal an anatomical or toxicological cause of death. Incidence rates range between 0.35 and 2.7 per 1000 person-years in the population-based studies and between 1.5 and 9.3 per 1000 person-years in selected cohorts. Seizure frequency appears to be an important factor in sudden unexpected death in epilepsy, although the exact pathogenetic mechanisms involved are unclear.