We investigated the distribution of memory (CD45RO+) and naive (CD45RA+CD62L+) CD4+ T-cells as well as CD8+ T-cells and total T-cells in the CSF of children with aseptic meningitis following measles-mumps-rubella (MMW) vaccination and those with enteroviral meningitis. Flow cytometric analysis of CSF cells was performed in 12 children with MMR vaccine-associated meningitis and 11 children with enteroviral meningitis. Percentages of total T-cells, CD4+ and CD8+ T-cells and monocytes in CSF of patients from the two groups were not significantly different. The majority of CD4+ T-cells in the CSF of both patient groups were of memory phenotype. Percentages of CSF naive CD4+ T-cells were increased in children with aseptic meningitis following MMR vaccination. Further studies focused on the more detailed immunophenotyping of CSF cells are needed to fully establish the usefulness of flow cytometry in the diagnostic workup of inflammatory CNS diseases in children.