Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disorder of the central nervous system (CNS) resulting from infection of oligodendrocytes by JC virus. Although all patients immunocompromised by any congenital, acquired, or iatrogenic condition are at risk, the population which currently accounts for the majority of new cases is that infected with the human immunodeficiency virus (HIV). Though the clinical/radiologic presentation is characteristic, biopsy confirmation is necessary, as these patients are at risk for other primary CNS disorders which may produce similar clinical findings. Immediate assessment of tissue adequacy by cytologic smear is generally preferred in these specimens due to its relative reduced risk of disease transmission when compared to conventional frozen section. We report here the cytologic findings seen in touch imprints and squash preparations of 16 cases of PML, all occurring in HIV-positive patients and obtained by stereotactic guided needle biopsy. Typical cytomorphologic findings are described and correlated with histologic sections. In addition, features useful in the exclusion of other differential diagnostic possibilities are discussed.