Abstract： Objective To explore the clinicopathological characteristics,diagnosis,treatment and prognosis of malignant rhabdoid tumor (MRT) in infants.Methods The clinical data,histopathological and immunohistochemical examinations were analyzed for 5 MRT patients from January 2009 to December 2014.Results There were 3 boys and 2 girls with an average age of 70 days.And the diagnostic time was 1 day to 330 days.Tumors were detected in kidney (n =1) and skin soft tissue (n =4).The neoplastic stages were Ⅰ (n =1) and Ⅳ (n =4).All of them underwent local wide resection with regional lymph node dissection.Tumors had infiltrated the surrounding tissue with intravascular tumor emboli in 3 patients.Classified as stage Ⅳ,they abandoned treatment,recurred at Day 5-7 and died at Day 14-28 post-operation.And the average age was 21 days.In one patient with renal MRT,intravascular tumor emboli were detected intraoperatively in renal cortex and multiple pulmonary tumor nodules visualized on computed tomography (CT).Tumor was classified as stage Ⅳ.After 5 cycles of chemotherapy,metastatic lung tumor expanded.This patient survived for 6 months postoperatively.In another patient with perineal MRT,tumor showed no invasion into the surrounding tissue and no intravascular emboli and it was classified as stage Ⅰ.Without chemotherapy,this patient survived without recurrence or metastasis up to 3 years postoperatively.Among 4 cases of stage Ⅳ MRT,75％ (3/4) died within 6 months and 100％ within 1 year postoperatively.The mortality rate rose with the stage of tumor.The histological characteristics of MRT were rhabdoid cells with eosinophilic cytoplasm often containing hyaline inclusions,eccentric oval nuclei and prominent nucleoli.Immunohistochemically,vimentin,CK and EMA were positive while INI1 was negative.Conclusions As a rare highly aggressive malignancy in young children with early metastasis and recurrence,MRT is usually in advanced stage at the time of diagnosis and its outcomes are poor.Early total resection often yields a longer survival.