The nervous system is profoundly affected by acquired immunodeficiency syndrome. Nervous system pathology is responsible for the initial symptoms in 10 percent of AIDS patients and is found at autopsy in 75 percent of patients with AIDS. Human immunodeficiency virus can directly infect the brain, producing a dementia. It can also cause aseptic meningitis, spinal vacuolar myelopathy, distal symmetric peripheral neuropathy or inflammatory demyelinating polyradiculoneuropathy. The last condition may be effectively treated with plasmapheresis. Neurologic disorders due to other infectious agents are also common in AIDS patients.