We studied a 67-year-old female who suffered from poylmyositis associated with primary biliary cirrhosis (PBC). Liver dysfunction was revealed by a screening test. Antimitochondrial antibodies (AMA) and antinuclear antibodies were positive. Liver biopsy was compatible with PBC (Scheuer stage I). Four years later she showed severe weakness and atrophy on her four extremities. Laboratory examination showed a creatinine kinase level of 312 IU/l, IgM 416 mg/dl, and AMA titer 1:320. Muscle biopsy findings were compatible with polymyositis. Electron microscopic examination disclosed diffuse increase of mitochondria in subsarcolemma and intermyofibrils, which has not been reported until now in polymyositis associated with PBC.