A study of 38 boys with progressive muscular dystrophy indicated that they were functioning at lower intellectual levels than were a variety of control groups. Their academic achievement, however, was well correlated with their mental ages. No progressive mental deterioration was found. There was no relationship between tested intelligence and severity of illness, length of illness, or age of onset of illness. The only factor associated with lowered intellectual abilities was the presence of childhood progressive muscular dystrophy. A hypothesis was advanced concerning the possible nature of muscular dystrophy and its relation to intellectual retardation. Much very basic research is needed before such a hypothesis can be accepted.