Muscular dystrophies are a wide range of muscle disorders related to the congenital or genetically determined absence of certain essential muscle fiber components (e.g., dystrophin). In most patients, the major symptoms are of muscle weakness starting in childhood and early adolescence. Certain muscular dystrophies are also known to affect organs other than skeletal muscle, including the heart. The rate of progression of the muscular dystrophies depends on the type of dystrophy. While some progress slowly, others confine the patient to a wheelchair within a few years. Significant advances in the genetics of these conditions and further understanding of the pathogenesis will undoubtedly result in the effective treatment for these devastating muscle conditions.