A 43-year-old Caucasian homosexual man with AIDS presented with blurring of vision, change of personality, and memory loss in March 1999. He had first been admitted 2 months previously for treatment of Pneumocystis jiroveci pneumonia. A magnetic resonance imaging scan on admission showed multiple white matter lesions involving both subcortical cerebral hemispheres and cerebellar regions, with no mass effect or surrounding edema. JC virus was detected by nested polymerase chain reaction in the cerebrospinal fluid. These findings were diagnostic of progressive multifocal leukoencephalopathy (PML). His CD4 count was 34 cells/mL, and his HIV ribonucleic acid level was 800,789 copies/mL. He was treated with a combination antiretroviral therapy. He was last reviewed in October 2011. He was fully independent socially and mentally, but he still had some residual neurologic signs with right-sided homonymous hemianopia and visual agnosia. His HIV ribonucleic acid level was undetectable, and his CD4 count was 574 cells/mm(3). Although the median survival of patients with PML was poor before the antiretroviral therapy era, our patient, who is now aged 55 years, is still alive 12 years after the diagnosis. The diagnosis of PML and differential diagnosis of focal neurologic signs in HIV-positive patients are discussed in this case report.