Nonprogressive congenital myopathies are usually classified according to structural or ultrastructural changes in the muscle fibres. In our material cases without specific structural characteristics but with an abnormal distribution and size of one fibre type, and dystrophic changes with or without fibre type changes are far more numerous. 15 cases are reviewed: Congenital dystrophy (4 cases); congenital dystrophy with complete lack of type II fibres ; fibre type disproportion with predominance of abnormally small type I fibres ; fibre type disproportion with predominance of small and large type I fibres and rare small type II fibres (1); type II hypotrophy with cardiomyopathy ; type II hypotrophy without cardiac or cerebral abnormalities . Ultrastructural investigation shows unspecific changes mainly of myofilaments. The EMG is "myopathic" with normal interference pattern and short polyphasic unit potentials.