Three adult brothers showed multiple peripheral nerve entrapments. Most severely involved were the median nerves at the carpal tunnel and the ulnar nerves at the cubital tunnel. Sural nerve biopsy from patient 2 showed slight Wallerian degeneration and extensive Renaut bodies. By electron microscopy, vacuolated fibroblasts with membranous material and zebra bodies were present in the epineurium and between skeletal muscle cells. Copious mucopolysaccharides found in the urine of all patients and the increased urinary GAG/GAG fragment ratio in patient 1 were typical of mucopolysaccharidosis. In vitro fibroblast typing by the corrective factor method showed the defect of the Hunter syndrome in patient 1. These patients are unusual phenotypical variants of the Hunter syndrome (mucopolysaccharidosis II). Mucopolysaccharidosis should be searched for in patients with unexplained multiple peripheral nerve entrapments.