Purpose To investigate the clinicopathological characteristics,diagnosis and differential diagnosis of benign metastasizing leiomyoma (BML).Methods The clinicopathological data in 6 patients with BML were collected.All cases of BLM were investigated by HE and immunohistochemistry of EnVision method.Results All cases were female,with age of 33 -65 years,and had undergone myomectomy.5 cases had lung metastasis,including abdominal wall metastasis and spinal metastasis in each of the 1 cases,and another case had inguinal metastasis.Morphology showed that the tumor cells were spindle without obvious atypia,nuclear mitoses and necrosis,some cases were cellular.Immunohistochemical staining showed that the tumor cells were positive for SMA,SM-MHC,desmin,ER,PR,vimentin,while negative for S-100,CD117,CD34.Ki-67 label index were less than 5％.3 patients were alive with tumor and 3 patients were alive without tumor in the follow up of 18,28,40,31,36,80 months.Conclusion BML often occurs in female patients that undergone uterine myomectomy.The lung is the most common site of metastasis,often accompanied by other sites.The disease progresses slowly,and most patients have a longer survival time.