Histochemical and electron microscopic studies were performed in an attempt to clarify the muscle pathology in an 18-year-old man with Fabry disease, showing proximal limb muscle atrophy, and his 52-year-old mother, who is a Fabry carrier with hypertrophic cardiomyopathy. Despite the relatively mild myopathic changes revealed by histochemistry, electron microscopy demonstrated the widespread accumulation of abundant lamellated bodies in myofibers, associated with increased glycogen granules and autophagic vacuoles. The cardiac muscle of the proband's mother revealed a mosaic pattern of normal-appearing and hypertrophic myofibers containing a number of ring-like, lamellated bodies. Although further studies are necessary to support our findings, skeletal muscle is apparently involved in patients with Fabry disease, and a mosaic pattern of cardiac muscle involvement possibly reflecting Lyonization, may be one of the characteristic findings of a Fabry disease carrier.