Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease resulting from infection of oligodendrocytes with JC virus. PML was a rare disease, but nowadays not uncommon as AIDS prevailed. Histopathologic features of the affected lesion shows infiltrations of foamy macrophages and hyperchromatic, pleomorphic, reactive astrocytes that may raise the suspicion of a brain tumor. We recently met with 3 cases of PML. Two of the patients had AIDS and the other had been treated for lymphoma. All cases were diagnosed by histopathologic examination in stereotactic brain biopsies.