Clinical characteristics recognized in five cases with Ullrich's disease included muscle weakness and wasting, striking contracture of proximal (sclerotic) joints and hyperflexibility of distal (atonic) joints since an early infantile stage, and slowly progressive course. The biopsied muscles demonstrated myopathic changes including a remarkable variation in fiber size, notably proliferated endomysial connective tissue, increased myofibers with centralized nuclei and a few necrotic fibers with active phagocytosis. On histochemical examination, no specific intracytoplasmic structural abnormalities such as nemaline bodies, cores and myotubes were recognized. Although both type 1 and 2 fibers were distributed in checkerboard pattern in most muscle fascicles, type 1 fiber predominance or type 2 fiber deficiency was common in severely damaged muscles, suggesting the presence of some kind of neural influence exerting on the myopathic process as the disease progressed. Since it still remains uncertain whether this disorder belongs to the muscular dystrophies, or to other neuromuscular or mesodermal diseases, we would rather label it Ullrich's disease then Ullrich's muscular "dystrophy" until its pathogenesis becomes clear.