Lymphomatous polyneuropathy. Biopsy of clinically involved nerve and successful treatment. We present a patient with large-cell lymphoma in remission who, over several weeks, developed widespread multifocal polyneuropathy. There was involvement of all four limbs, most severely the left upper extremity that had become useless. Biopsy of the left saphenous nerve within an area of sensory loss showed lymphoma in the endoneurium. There was no other evidence of recurrent lymphoma despite extensive investigation, including bone marrow, lumbar puncture, magnetic resonance imaging of the spine, and computed tomography of the abdomen and pelvis. Intensive systemic chemotherapy was accompanied by nearly complete recovery. Biopsy of a symptomatic nerve is preferable to routine sural nerve biopsy in this condition because of its patchy distribution. Treatment with systematic chemotherapy can be effective. 