• Radial compression neuropathy developed in four patients with advanced Parkinson's disease. Electrodiagnostic studies in two patients documented the upper middle part of the arm as the site of nerve injury. The conditions of three patients improved over four months. One markedly disabled, bradykinetic patient had a permanent flexion deformity of the wrist and hand. Radial compression neuropathy may be an initiating factor in the development of hand deformities in patients with late-stage parkinsonism.