Human immunodeficiency virus (HIV) infection has expanded to become a global pandemic which threatens health in most areas of the world, and is now the leading cause of death among some segments of the population. Infection with HIV-1, a member of the lentivirus subfamily of retroviruses, produces a wide spectrum of clinical manifestations, ranging from asymptomatic infection to severe, life-threatening opportunistic infections. The prevalence of HIV dementia is only 0.4% during the asymptomatic phase of infection. In patients with AIDS, dementia develops in 15-20%. The diagnosis of HIV dementia is established by a history of a progressive cognitive or behavioral decline with apathy, memory loss, or slowed mental processing and by appropriate ancillary studies. HIV-1 associated vacuolar myelopathy (HIV myelopathy) is characterized by a vacuolar degeneration affecting predominantly the thoracic spinal cord. Patients may have multiple concurrent opportunistic processes, or opportunistic processes may coexist with HIV-related neurological disorders.