OBJECTIVE To determine the incidence of pleocytosis in patients experiencing status epilepticus (SE), regardless of seizure type or cause. METHODS A retrospective medical chart review. METHODS Columbia-Presbyterian Medical Center, New York, NY. METHODS Of 217 patients seen by the Neurology Service for SE during a 3-year period, 138 had a cerebrospinal fluid (CSF) analysis performed and were included in the study. All seizure types and etiologies were included. METHODS Status epilepticus was defined as a seizure or a series of continuing seizures lasting longer than 30 minutes. An abnormal CSF specimen was defined as a white blood cell (WBC) count of 6 x 10(6)/L or greater or one or more polymorphonuclear leukocytes present. RESULTS Overall, 22.5% of patients demonstrated abnormal WBC count or morphology. There were 21 patients (15%) with a WBC count of 6 x 10(6)/L or greater, and another 10 patients with a normal WBC count, who had polymorphonuclear leukocytes present. Among patients with illnesses usually associated with pleocytosis (such as meningitis or acute head trauma), a large proportion had abnormal CSF WBC counts. Among patients with conditions usually associated with normal CSF (including idiopathic epilepsy), a small proportion had abnormal CSF WBC counts, and the abnormalities were less severe. The highest CSF WBC count in patients with no acute insult was 28 x 10(6)/L. CONCLUSIONS The most important influence on the CSF WBC count is the underlying cause of the SE. Although minor elevations in WBC count can occur after SE of any type, pleocytosis should not be attributed to SE alone unless all other causes have been eliminated.