Summary:We report a patient with progressive multifocal leukoencephalopathy (PML) after autologous stem cell transplantation (SCT) for non-Hodgkin's lymphoma (NHL). This is an unusual association, and to date only seven cases have been reported. This is the first case of PML after SCT treated with cidofovir, and the fifth case treated with this drug in a patient without human immunodeficiency virus (HIV) infection. In the previous four patients treated with cidofovir the outcome was discouraging, as was the case in this patient.