Status epilepticus (SE), or status seizure, is a medical condition consisting of a single seizure lasting more than 5 minutes, or 2 or more seizures within a 5-minute period without the person returning to normal between them. Previous definitions used a 30-minute time limit. The seizures can be of the tonic–clonic type, with a regular pattern of contraction and extension of the arms and legs, or of types that do not involve contractions, such as absence seizures or complex partial seizures. Status epilepticus is a life-threatening medical emergency, particularly if treatment is delayed.

Status epilepticus may occur in those with a history of epilepsy as well as those with an underlying problem of the brain. These underlying brain problems may include trauma, infections, or strokes, among others. Diagnosis often involves checking the blood sugar, imaging of the head, a number of blood tests, and an electroencephalogram. Psychogenic nonepileptic seizures may present similarly to status epilepticus. Other conditions that may also appear to be status epilepticus include low blood sugar, movement disorders, meningitis, and delirium, among others. Status epilepticus can also appear when tuberculous meningitis becomes very severe.

Benzodiazepines are the preferred initial treatment, after which typically phenytoin is given. Possible benzodiazepines include intravenous lorazepam as well as intramuscular injections of midazolam. A number of other medications may be used if these are not effective, such as phenobarbital, propofol, or ketamine. After initial treatment with benzodiazepines, typical antiseizure drugs should be given, including valproic acid (valproate), fosphenytoin, levetiracetam, or a similar substance(s). While empirically-based treatments exist, few head-to-head clinical trials exist, so the best approach remains undetermined. This said, "consensus-based" best practices are offered by the Neurocritical Care Society. Intubation may be required to help maintain the person's airway. Between 10% and 30% of people who have status epilepticus die within 30 days. The underlying cause, the person's age, and the length of the seizure are important factors in the outcome. Status epilepticus occurs in up to 40 per 100,000 people per year. Those with status epilepticus make up about 1% of people who visit the emergency department.