The introduction of highly active antiretroviral therapy does not seem to have altered the incidence of progressive multifocal leukoencephalopathy (PML) in HIV infection. Moreover, the occurrence of a HIV-related leukoencephalopathy, called not determined leukoencephalopaties (NDLE), has been reported. As neuropsychological impairment remains highly prevalent in HIV infection, the aim of this study is to describe the neuropsychological profile of PML and NDLE patients, analyzing the time-related changes. Clinical and neuropsychological data from 32 patients (17 PML, 15 NDLE) were compared with two control groups: (1) asymptomatic HIV+ patients without magnetic resonance imaging evidence of leukoencephalopathy; (2) age-/gender-/education-matched healthy subjects. Patients with rapidly worsening PML were significantly impaired on all neuropsychological tests, while PML with more benign course and NDLE groups showed a dysexecutive pattern of impairment. Asymptomatic HIV+ subjects showed mild and isolated cognitive deficits, without functional impact. Cognitive impairment should therefore be considered a key feature from HIV infection diagnosis.