Acute disseminated encephalomyelitis (ADEM) is a demyelinating disorder of the central nervous system with an acute clinical onset and a wide variability in severity and outcome. It usually follows a viral infection or an immunization and is thought to be immuno- mediated. We report a case of ADEM with a dramatic clinical onset in an autologous peripheral blood stem cell transplant (PBSCT) recipient for non-Hodgkin's lymphoma who developed the neurologic syndrome 12 days after PBSC reinfusion. This is the first report of ADEM in the setting of autologous PBSCT, a therapeutic procedure performed with increasing frequency in a wide variety of hematologic and solid malignancies.