A group of patients with HIV infection in various stages of the disease was studied with regard to CSF, neuroradiological and neuropsychological aspects. A considerable number of them showed signs of CNS involvement, as revealed by abnormalities in all the three fields investigated, despite a frequently unremarkable neurological examination. The findings of CSF alterations, neuroradiological abnormalities and selective cognitive impairment in the absence of opportunistic infections of the CNS support the hypothesis of an early and direct action of HIV on the nervous system.