Objective To study the characteristics and treatment of 33 patients with polymyositis and dermatomyositis. Methods The clinical and pathological findings of 33 patients with polymyositis and dermatomyositis were ratrospectively analysed.Results The main clinical presentation of polymyositis and dermatomyositis included amyosthenia,musculal tenderness,elevation of serum enzymes,accompanied by abnormal electromyography and muscular pathology.A total efficacy rate of 89.2% was achieved after treatment with corticosteroid and immunodepressants.Conclusions The prognosis of polymyositis and dermatomyositis is related to its classification and then timing of the treatment.Early effective treatment can improve the prognosis.