Status epilepticus (SE) will occur in 50,000 to 60,000 individuals in the United States annually: one third as the presenting symptom in patients with a 1st unprovoked seizure or with epilepsy, one third in patients with established epilepsy, and one third in individuals with no history of epilepsy. The greatest number of cases will occur in children, although the risk is equally high in the over-60 population. In patients with epilepsy, SE is more likely to occur in those with partial seizures and in those with remote symptomatic epilepsy. The presence of a preexisting neurologic abnormality is associated with an increased risk of SE in those with acute systemic insults. There is a high mortality reported, but this is related predominantly to the underlying condition. The 1 to 2% mortality attributed to SE probably reflects an overestimation of the risk. There is an increased risk of seizures and of intellectual dysfunction following the occurrence of an episode of SE, although the causal association is not clear. Individuals with epilepsy who experience an episode of SE probably have a lower likelihood of remission of epilepsy.