The fantastic advances in fundamental research into muscular dystrophy over the past few years have led to the discovery of a cytoskeleton protein called dystrophin and a group of associated and analogous molecules. The understanding of their molecular structure and the modes of genetic and functional regulation have forced us to take a new look at our concept of the pathogenesis of muscular dystrophy. Today, the group of diseases called X-linked hereditary muscular dystrophies must now be conceived in light of a deficiency in dystrophin. The exact physiopathology of the process involved is not yet fully understood but most undoubtedly, although the lack of dystrophin can trigger the disease, the deficiency cannot in itself impede muscle contraction. As a result of these discoveries, diagnostic methods have changed drastically, genetic counselling has become more precise, and most importantly, new treatment rationales can call upon pharmacological processes capable of stopping disease progression. Genetic therapy is another approach. The aim is to provide the deficient cells with the capacity of synthesizing normal dystrophin or an analogous molecule, thus halting the cascade of events leading to necrosis. The transfer of the technical means which have made these fundamental advances in basic research possible to successful clinical applications in the treatment of muscular dystrophy will be another of the lessons to be learned from dystrophin.