Abstract A group of 17 children has been studied. They presented at birth or in the first year of life clinical symptoms and signs suggestive of muscular dystrophy. The electromyographic criteria of the diagnosis and the evolution of muscular dystrophy are studied by means of longitudinal studies. The relative value of the electrical parameters are defined for these early clinical cases. From this group it has been possible to separate 5 children who presented with particular symptoms and signs. The others are probably congenital or early cases of the Duchenne type of muscular dystrophy. The 5 particular cases have been called “myopathia precocissima”. This disorder is congenital, probably autosomal recessive, and predominant in girls. Clinically it is possible to distinguish between a benign and a malignant type. The latter type is characterised by the presence of arthrogryposis, a severe muscle atrophy and involvement of the respiratory muscles. Death is early, during the first year of life. The benign type presents with a generalised muscular hypotonia, suggestive of hypotonia of central origin or of “amyotonia congenita”. The electromyographic examination shows signs of a rapidly evolving and severe myogenic disorder. The muscle biopsy shows an early infiltration of collagen tissue together with minor lesions of the muscle fibres. These findings are unusual in the Duchenne type of muscular dystrophy and suggest that the condition is a specific disease entity in the group of the congenital myopathies. The authors have preferred for this group the name of “myopathia precocissima”.