A 35-year-old caucasian man developed mild and transient signs of chronic graft-versus-host disease (GVHD) 5 months after bone marrow transplantation. At 16 months he presented with painful cramps in hands, feet, and truncal muscles. Electrophysiological studies revealed generalized sensory neuropathy. There was occasional fasciculation and high frequency motor units during involuntary muscle contractions, and agonist/antagonist cocontractions of peripheral muscle groups (non-continuous). A sural nerve biopsy showed Schwann cells and macrophages with myelin debris, and Schwann cell stacks with collagen pockets. The patient's symptoms responded to treatment with glucocorticoids and azathioprine. We propose that this patient's incapacitating polyneuropathy was a major manifestation of chronic GVHD, suggesting that the peripheral and possibly central nervous systems can be targets of chronic GVHD.