Progressive multifocal leukoencephalopathy (PML) typically affects the CNS white matter of the central nervous system. We present an human immunodeficiency virus-infected patient with polyomavirus JC infection restricted to granule cell neurons of the cerebellum and with corresponding neurological symptomatology. Magnetic resonance imaging demonstrated cerebellar atrophy without white matter lesions and stereotactic biopsy showed selective infection of the cerebellar granular cell layer, with preservation of Purkinje cells and absence of classic progressive multifocal leukoencephalopathy histopathology in underlying white matter. Evolution over 8 years was marked by symptomatic improvement corresponding to highly active antiretroviral therapy (HAART), with modest increase in CD4(+) T-cell counts. We propose to call this novel syndrome JCV granule cell neuronopathy (JCV GCN).