Progressive multifocal leukoencephalopathy (PML) is a rare opportunistic infection of the brain caused by reactivation of the JC virus, which can lead to a lytic infection of oligodendrocytes. We report a patient with HIV who developed PML. Progressive multifocal leukoencephalopathy (PML) is a rare opportunistic infection of the brain caused by reactivation of the John Cunningham virus (JCV), which can lead to a lytic infection of oligodendrocytes. Herein, we report the case of a patient with HIV who developed PML that presented as a progressive disturbance of consciousness and movement. The patient's clinical symptoms progressively deteriorated, and positive JC viral DNA in his cerebrospinal fluid (CSF) helped us diagnose him with PML. Magnetic resonance imaging (MRI) showed multiple asymmetric subcortical and deep white-matter lesions. Although we administered immunoreconstructive therapy, the patient's condition gradually worsened. Therefore, we suggest that PML should be considered if such lesions are found in MRIs of HIV patients.