Objective: Primary mediastinal yolk sac tumor, which is also known as endodermal sinus tumor, is a rare but lethal neoplasm and its prognosis is very dismal. The current treatment for this tumor is controversial, and chemotherapy combined with resection of residual lesions is adopted sometimes. We summarized the experience of seven primary mediastinal yolk sac tumors treated with platinum-based chemotherapy and extended resection in Peking University First Hospital.Methods: Clinicopathological data of the patients with primary mediastinal yolk sac tumor who received operation in Peking University First Hospital between August 2014 and August 2018 were collected and analyzed retrospectively.Results: We experienced seven primary mediastinal yolk sac tumors during this period. Computed tomography scan revealed an anterior mediastinal tumor in all the patients and all of them had markedly raised alphafetoprotein (AFP) and normal β-human chorion gonadotropin (β-HCG). Five patients underwent needle core biopsy before treatment, which showed a mediastinal yolk sac tumor. All of these patients received preoperative platinum-based chemotherapy and they all presented partial response according to computed tomography. Two other patients did not receive preoperative biopsy, so they directly underwent extended resection. All of the seven patients underwent operation successfully and two of them expe-rienced postoperative complications, including one with pneumonia and the other with atelectasis. R0 resection was achieved in six patients and R1 resection was achieved in the other patient. According to postoperative pathology, there were one microcyst subtype, one adenoid subtye, one giant capsule subtype and two hybrid subtypes. Surprisingly, there were no yolk sac tumor tissue in the other two patients after preoperative chemotherapy. All the patients received postoperative chemotherapy, excluded one patient who was unable to tolerate chemotherapy after operation. Three patients experienced postoperative pulmonary metastases within one year and two of them died soon. The other patient received chemotherapy and immunotherapy after recurrence and he was alive at the time of writing. Four other patients were alive without recurrence and metastasis.Conclusion: Primary mediastinal yolk sac tumor is rare and its prognosis is poor. A multimodality approach including adjuvant chemotherapy and resection of residual lesions is the optimal treatment and it may lead to long-term survival.