HIV-associated dementia will eventually develop in 15-20% of individuals with advanced HIV disease. It has become one of the leading causes of dementia in the young, with 10,000 new cases annually in the USA. The clinical syndrome includes progressive development of psychomotor slowing and memory impairment, eventually with brain atrophy and neurol loss. The pathology is characterized by infection of macrophages and microglia, marked activation of macrophages, and release of a variety of postinflammatory cytokines into the parenchyma. Antiretroviral therapy has impacted positively on the incidence rates, and at least partial reversal of neurologic deficits can be achieved in established dementias.