Nonconvulsive status epilepticus (NCSE) is difficult to diagnose in the obtunded/comatose patient. Such patients often have other serious medical conditions, and the diagnosis is frequently delayed. We review criteria for diagnosis, treatment, and prognosis of NCSE in this setting. Terms that have been used to describe SE in obtunded/comatose patients without tonic-clonic convulsions include subtle generalized SE, electrographic SE, SE in comatose patients, generalized electrographic SE, non-tonic-clonic SE, subclinical SE, and NCSE. Sometimes the same term has been used when describing different disorders, and different terms are often applied for the same entity. The incidence of NCSE in obtunded/comatose patients is uncertain. Clinically they may display subtle, intermittent focal or multifocal rhythmic movements suggestive of seizures; there may not be movements. NCSE can occur in a variety of disorders, including hypoxia, metabolic disturbances, and after convulsive seizures. A number of EEG patterns have been described in NCSE, and many of these are controversial, particularly as to whether they are ictal. These include periodic lateralized epileptiform discharges (PLEDS), bilateral independent PLEDS (BIPLEDS), periodic epileptiform discharges (PEDS), which can be either focal or generalized, and generalized triphasic waves (TWs). The diagnostic criteria for NCSE also are controversial, and there are no agreed-on criteria to diagnose NCSE in obtunded/comatose patients, nor is there consensus on how it should it be treated. Furthermore, outcome is poor, and several studies suggest that treatment may not be helpful.