The association between cytomegalovirus (CMV) infection and the development of Guillain-Barré syndrome (GBS) in the setting of allogeneic hematopoietic stem cell transplantation (alloSCT) has been reported only occasionally. We describe here a 23-year-old patient diagnosed with acute myelogenous leukemia who underwent a partially HLA-mismatched alloSCT and soon after developed GBS along with a CMV infection. Serum autoantibodies to several ganglioside antigens were concomitantly detected. Despite therapy with ganciclovir and plasma exchanges, the patient's clinical condition rapidly deteriorated, and he died 3 weeks later with persisting CMV antigenemia. Although a coincidental association cannot be excluded, it could be speculated that a pathogenetic link exists between the 2 disorders. In this sense, molecular mimicry between viral antigens and neural host tissues could be postulated as the hypothetical mechanism underlying the triggering of the autoimmune disease in the present case.