The analysis of cerebrospinal fluid (CSF) is described as the central nervous system equivalent of the complete blood count and the analogy is a good one. A CSF analysis provides a general index of neurologic health, and it often provides evidence of the presence of disease. Similar to a complete blood count, CSF analysis has reasonable sensitivity but low specificity. The possible alterations of CSF are relatively limited compared to the varieties of neurologic diseases that exist. Additionally, the type and degree of CSF abnormality seems to be related as much to the location of disease as to the cause or the severity of the lesion; meningeal and paraventricular diseases generally produce greater abnormalities than deep parenchymal diseases. Previous therapy may affect the type, degree, and duration of CSF abnormalities as well. The CSF abnormalities identified upon analysis are also dependent on the CSF collection site with respect to lesion location. CSF analysis only occasionally provides a specific diagnosis.