Muscular dystrophies due to calpain deficiency are the first example of a muscular dystrophy due to the mutation of a gene codifying for a non-structural enzymatic protein of unknown function and substrate.More than 70 mutations have been described in the gene structure, localized to chromosome 15. Although the time course and topography is fairly homogeneous, correlation between the different mutations and the phenotype has still to be analyzed. The age of onset of symptoms is usually between 8 and 14, with no difference between the sexes. There is a slow but uniformly progressive course starting in the pelvis and extending to the shoulder and the distal musculature. Almost all patients are confined to a wheelchair twenty years after onset of the disease. There is no facial, oculomotor or bulbar involvement and gemellar pseudohypertrophy is rare. However, a winged scapula and marked lumbar hyperlordosis is universal. No cardiac or cognitive changes have been observed. Muscle CT shows a pattern of atrophy, mainly of the posterior and medial muscle compartments and of the posterosuperficial group of the legs, which varies depending on the time the disorder has been present. This condition is the commonest etiological group of the dystrophy syndromes, especially of those of late infancy or juvenile onset, in the open populations studied to date. Muscle biopsy, stained by all methods available, is essential to rule out other types of progressive dystrophies secondary to deficiencies of structural proteins.