Objectives: To assess the etiology of cerebrospinal fluid (CSF) pleocytosis in critical care patients with seizure(s) or status epilepticus (SE). Many previous studies, some performed decades ago, concluded that CSF pleocytosis may be entirely attributable to seizure activity. Methods: We undertook a retrospective chart review of adult patients with an admitting or acquired diagnosis of seizure(s) or SE in critical care units at the Winnipeg Health Sciences Centre between 2009 and 2012. Patients were identified through a critical care information database at a tertiary care center. We limited our study to patients who had lumbar punctures at our center within 5 days of seizure(s) or SE. Results: Of 426 patients with seizures in critical care units, 51 met the inclusion criteria. Seizure subtypes included focal seizures (5 or 10%), generalized seizures (14 or 27%), and SE (32 or 63%). Twelve (seven with SE) of the 51 (24%) were found to have CSF pleocytosis. A probable etiological cause for the CSF pleocytosis was identified in all 12 cases. Conclusions: We conclude that seizures do not directly induce a CSF pleocytosis. Instead, the CSF pleocytosis more likely reflects the underlying acute or chronic brain process responsible for the seizure(s). This was not readily apparent in early studies without magnetic resonance imaging (MRI) of the brain and currently available laboratory investigations. An etiological cause of CSF pleocytosis must always be sought when patients present with seizures and it should never be assumed that seizures are the cause.