We report a generalized polyneuropathy coincident with the occurrence of graft-versus-host disease in four patients undergoing bone marrow transplantation and accompanying solid organ rejection (heart and kidney) in two patients. The neuropathy affected proximal and distal muscles, demonstrated hyporeflexia or areflexia, and usually had elevated CSF protein. Electrophysiologic studies did not meet strict criteria for demyelination. The signs of neuropathy improved after immunosuppressive treatment or simultaneous to the resolution of graft-versus-host disease or tissue rejection. Polyneuropathy must be considered as a potential complication of tissue transplantation.