Progressive multifocal leucoencephalopathy is an opportunistic JC virus-related pathology occurring in immunocompromised patients. We report a case of severe cellular immunodeficiency in a patient who underwent autologous bone marrow transplantation for acute myeloblastic leukemia, and who subsequently developed progressive multifocal leucoencephalopathy, an unusual pathology in this context. Progressive multifocal leucoencephalopathy was preceded by a peripheral demyelinating neuropathy. We discuss the possible link between these two neuropathies, the possible aggravation or activation from CMV infection, as well as the possible contribution of bone marrow purging in the resultant cellular immunodeficiency.