Three cases from 2 families had muscle weakness with predilection for distal extremities, predominantly affecting the tibialis anterior muscles, and onset in early adulthood. The disorder seemed to be inherited through an autosomal recessive trait. The EMG demonstrated a myopathic pattern and CPK was mildly elevated. The striking finding in their muscle biopsies was the presence of "rimmed" vacuoles which had acid phosphatase-positive autophagic activity and which contained numerous concentric lamellar bodies in various forms (myeloid and cabbage bodies). Despite rapid clinical progression, not only necrotic fibers with phagocytosis, as seen in Duchenne dystrophy, but also evidence of regeneration were virtually absent. Continuous destruction of myofibrils by activation of certain lysosomal proteolytic enzymes might be responsible for the production of atrophic fibers.