The spreading of human immunodeficiency virus (HIV) infection and its increasing scientific knowledge keep the medical staff involved with these patients in permanent need of updating themselves. The different neurologic manifestations caused by HIV are related to a variety of pathogenic mechanisms, as follows: immunodeficiency, autoimmunity, direct effects of the virus on the nervous system, and toxic and metabolic effects. The opportunistic infections are caused by the immunodeficiency due to the action of the virus on CD4+ T cells and on cells of the monocytic-macrophage lineage. Demyelinating polyradiculoneuropathy and polymyositis-like syndromes are related to autoimmune mechanisms involving, probably, the non-specific stimulation of T cells by viral proteins. The primary action of the virus on the nervous system brings out aseptic meningitis, cognitive dysfunction, dementia, vacuolar myelopathy and sensory polyneuropathy probably through liberation of neurotoxic products by the infected macrophages. Antiretroviral drugs and others used to treat patients with AIDS may also have neurotoxic effects. The better understanding of the neuropathogenesis of HIV infection will permit the use of new, and more specific, therapeutical options in the future as well as a more precocious control of its neurologic complications.