SYNOPSIS A case of infantile metachromatic leucodystrophy is described in which symptoms started at 1 year of age with weakness and hypotonus in the lower extremities. The electrophysiological status was typical of a polyneuropathy, showing fibrillation and a reduction of the nerve conduction velocity to 30%. of the average for normal children of the same age. Clinical signs of a central lesion and mental regression were not evident until a year later. Nerve biopsy showed metachromatic granules in the phagocytes and in the Schwann cells, confirming the diagnosis of metachromatic leucodystrophy. In peripheral neuropathy in infancy without obvious cause, a nerve biopsy is the most appropriate method for diagnosis of the metachromatic leucodystrophy.