Cerebrospinal fluid (CSF) analysis very frequently makes the difference to the diagnosis, not only in relation to infections but also in other diseases of the nervous system such as inflammatory, demyelinating, neoplastic and degenerative diseases. The authors review some practical and important features of CSF analysis in infectious diseases of the nervous system, with regard to acute bacterial meningitis, herpetic meningoencephalitis, neurotuberculosis, neurocryptococcosis, neurocysticercosis and neurosyphilis.