We performed extended resection of primary mediastinal undifferentiated carcinoma, together with the superior vena cava and the upper lobe of the right lung, after effective induction chemoradiation therapy based on the results of a chemosensitivity test. Pathological examination of the resected specimen revealed that almost all of the tumor cells had died. The patient received adjuvant chemotherapy and has remained free from disease progression for 27 months since his operation. Our experience supports the effectiveness of an aggressive approach, in the form of chemosensitivity test-guided induction therapy, to treat this high-grade malignant disease, despite the risk of cancer dissemination.