Carpal tunnel syndrome (CTS) is very uncommon in childhood. Sixty-five cases are reported in the literature, principally due to metabolic diseases. In Mucopolysaccharidoses, prospective studies (Wraith and Alani, 1990) found a bilateral CTS in about 90%. We report four cases of Mucopolysaccharidoses, diagnosed on clinical and biological data (two cases of Hurler disease, and two cases of Hunter disease), in children aged less than five years. Each child had claw hands, without thenar atrophy. Median nerve conduction studies and electromyography confirm the CTS. Motor and sensory nerve conductions are normal in other nerves. Concentric needle studies show in two cases, on abductor pollicis brevis, spontaneous activities as repetitive discharges, fasciculations and multiplets. Median nerve stimulations reveal responses with late potentials during 70 ms due to reinnervation. The physiopathology of those carpal tunnel syndromes is discussed.