In patients with HIV infection, disease due to CMV depends on reactivation of the virus. Such reactivation usually occurs at an advanced stage of the disease, when there is severe immunodepression and the CD4+ leukocyte count is < 100/ml. CMV infection is seen clinically as three syndromes: 1) encephalitis with or without associated meningitis and/or ventriculitis. 2) polyradiculomyelitis affecting the lumbosacral roots, and 3) multifocal senso-motor neuropathy. Diagnosis depends on showing the virus to be present in the CSF, by detecting the early CMV antigen or by conventional culture. There are marked differences between encephalitis, polyradiculomyelitis and multifocal neuropathy in the rentability of viral culture. Whilst in encephalitis CMV culture is negative in most patients, in polyradiculomyelitis the sensitivity of viral culture may be 50-60% and in multifocal neuropathy 15%. The treatment indicated is with ganciclovir or foscarnet. Results depend on the type of neurological disease, degree of involvement when treatment is started and an history of extracerebral CMV infection previously treated with these drugs.