Various findings prove the neurotropism of the human immune deficiency virus (HIV). Besides an aseptic meningitis at the time of seroconversion and polyradiculoneuropathies clinical and neuropathological studies focus on subacute encephalitis leading to dementia and focal neurological complications. Therapeutic strategies, various considerations concerning the pathogenesis of other subacute, chronic and slow virus infections of the nervous system as well as prophylactic implications become more and more important.