AbstractPeripheral nerve dysfunction (PND) was found in as many as 43% of our patients with human T‐cell lymphotropic virus type I (HTLV‐I)–associated myelopathy (HAM/TSP). To evaluate the PND further we biopsied the sural nerve in 6 patients. The histological features were varying degrees of demyelination, remyelination, axonal atrophy and degeneration, and perineurial fibrosis. “Globule” or “sausage” formation was prominent in two of the specimens. Inflammatory infiltrates were absent. No deposits of IgG, IgM, IgA, or complement were detected in the biopsies. No viral antigen or proviral DNA was detected. It is proposed that the PND and the histological findings noted are part of HTLV‐I–associated disease and not an unrelated disorder. The pathogenesis of the PND remains unclear. There was no evidence of direct viral infection. The histological findings could represent primary changes induced by viral‐triggered release of soluble factors, such as cytokines or secondary changes to more proximal disease, e.g., root involvement. © 1993