Myotonic dystrophy is an inherited disorder of muscle weakness and wasting characterized by sustained involuntary muscle contractions. These involuntary contractions arise in response to voluntary muscle use or percussion of the muscle. The disease was described by Steinert in 1909; it is also called myotonia atrophica. Clinically myotonic dystrophy is classified as a muscular dystrophy although the disease mechanism is distinct from that of the other muscular dystrophies. The familial pattern of inheritance is similar to that of myotonia congenita (Thomsen, 1876) and paramyotonia congenita (Eulenburg, 1886). Myotonic dystrophy is distinct in having widespread effects throughout the systems of the body. That this disease primarily affects muscle and not nerve was shown by Denny-Brown and Nevin in 1941. The tendency of the disease to become more severe with successive generations, called anticipation, was recognized by Fleischer in 1918. The genetic basis for the disease was elicited in 1992.