The myotubular myopathy is an X-linked centronuclear myopathy characterized by severe neonatal hypotonia and generalized muscle weakness which most frequently results in the premature death of the newborn infants by respiratory failure. The characteristic muscle histopathology consists in centrally positioned nuclei in most muscle fibers. In 1996, the gene responsible for the disease, MTM1, was identificated in Xq28 region. Since then, more than hundred mutations have been isolated. Genotype - phenotype correlation is complex because mutations are found along the entire coding sequence of the MTM1 gene. Most mutations are associated with very severe phenotype with death before the first year of life, however a milder phenotype has been individualized. It is important to be aware of the existence of such milder MTM phenotype because in those patients a very mild expression permit normal life into adulthood.