The acquired immunodeficiency syndrome (AIDS) dementia complex is a frequent and devastating complication of infection with human immunodeficiency virus-type 1 (HIV-1). Features of the AIDS dementia complex include decreased memory, the inability to concentrate, apathy, and psychomotor retardation. Typical neuropathologic findings include gliosis, focal necrosis of neurons, perivascular inflammation, formation of microglial nodules, multinucleated giant cells, and demyelination. That HIV-1 is the direct cause of this neurologic syndrome is strongly supported by the available evidence. In addition, several studies have identified the monocyte-macrophage as the predominant cell type in the brain infected with HIV-1. However, the mechanisms by which the infected monocytes-macrophages mediate neurologic dysfunction and destruction have not been elucidated.