The aim of the present study was to define the cellular composition of ventricular, as compared with lumbar, cerebrospinal fluid (CSF) in patients with non-inflammatory neurological disorders (NIND). We addressed this issue by determining the cellular composition of lumbar CSF from patients with normal pressure hydrocephalus (NPH) who were undergoing lumbar CSF drainage during evaluation for shunting procedures, and evaluating ventricular CSF from a subset of these who underwent subsequent placement of ventriculoperitoneal shunts. We determined the cellular composition of lumbar CSF from 18 patients with NPH, and found that the leukocyte differentials, and relative proportions of CD4+ and CD8+ central memory (TCM), effector memory (TEM) and naive cell (TNaive) populations, were equivalent to those found previously in studies of CSF from patients with NIND. We further evaluated cells in the ventricular CSF of five patients who had previously undergone lumbar drainage. Leukocyte differential counts, as well as CD4+ and CD8+ TCM, TEM, and TNaive proportions, were equivalent in matched ventricular and lumbar CSF samples. These observations support the hypothesis that leukocytes enter the CSF in a selective fashion, at its site of formation in the choroid plexus. The results implicate CSF T cells in the immune surveillance of the central nervous system.