In October 2007, a 41-year-old human immunodeficiency virus (HIV)–positive Brazilian woman was admitted to the hospital because of mild gait disturbance and difficulty in memory and concentration. She had a recent history of weakness, oral candidiasis, and weight loss. Neurologic examination revealed brisk tendon reflexes in the upper and lower limbs, sluggishness of ocular persecutory movements, unsteady gait, and slowness of alternated fast movements. A brief neuropsychological assessment of the patient revealed psychomotor slowness and diminished verbal fluency (Table). Her CD4 cell count and HIV viral load were 71/μL and 851.569 copies/mL (5.9 log), respectively. Brain magnetic resonance imaging (MRI) revealed diffuse white matter abnormalities without gadolinium enhancement (Figure, A). Cerebrospinal fluid analysis revealed 2 cells/μm3 (100% mononuclear), a glucose level of 46 mg/dL (to convert glucose to millimoles per liter, multiply by 0.0555), and a protein level of 0.7 g/dL (to convert protein to grams per liter, multiply by 10.0); the results of JC virus DNA polymerase chain reaction were negative. Two transcriptase nonnucleoside inhibitors and 1 protease inhibitor were prescribed. The patient was followed up monthly, and clinical improvement was apparent soon after antiretroviral therapy. A new neuropsychological assessment performed 6 months later showed marked improvement in all tests. At this time, the CD4 cell count was 139/μL and the HIV viral load was undetectable. Brain MRI performed in the seventh month of therapy showed marked improvement of white matter abnormalities seen in the baseline assessment (Figure, B). During this time, the patient returned to all of her daily activities.