The histopathological lesions of ovine congenital progressive muscular dystrophy (CPMD) were characterized by myofiber hypertrophy, focal myofibrillar degeneration, formation of peripheral and central sarcoplasmic masses devoid of myofibrils and internal nuclei often in chains. Progressive loss of myofibrils was associated with atrophy of the fiber and eventual collapse of the sarcolemma. The process was polyphasic, consequently in mature lesions there was great variation in fiber diameter. Split fibers were common but ring fibers occurred rarely. Myofiber loss was associated with fatty or fibrous tissue replacement. Only type I (red, slow twitch, oxidative) fibers were affected and there was no histological evidence of effective regeneration. Ovine CPMD has many histopathological features in common with dystrophia myotonica in humans.