We describe a kindred with a rare autosomal dominant myopathy limited to the limb-girdle muscles, beginning insidiously any time from the late second through the sixth decades and followed by slow progression. Pelvifemoral precedes scapulohumeral weakness, and proximal appendicular involvement antedates limited distal paresis. Expressivity varies and includes an asymptomatic myopathy (preclinical or subclinical) and a nonmanifesting carrier state that extends well into the eighth decade. A variety of nonspecific changes are present in muscle on light, enzyme histochemical, and electron microscopic examination; of these changes, "rimmed" or autophagic vacuoles are the most characteristic. We identified one very similar previously reported genealogy. The similarities between the two unrelated families clearly establish this dystrophic process as a distinct genetic entity; their differences suggest genetic heterogeneity.