We herein report a 52-year-old man infected with human immunodeficiency virus (HIV) who was referred to our hospital due to the development of severe neurocognitive disorders and bilateral leukoencephalopathy. He has been treated with antiretroviral agents for 17 years, but low-level viremia has been detected consistently prior to admission. Drug resistant testing of the serum and the cerebrospinal fluid (CSF) both demonstrated a M184V mutation. A brain biopsy revealed perivascular CD8(+) T-lymphocyte infiltration, leading to the diagnosis of CD8 encephalitis. The clinical symptoms improved drastically after changing to a nucleoside reverse transcriptase inhibitor sparing regimen, which subsequently decreased the HIV viral load to an undetectable level in both the serum and CSF.