Unknown primary large cell neuroendocrine carcinoma (LCNEC) in the mediastinum is extremely rare. In this report, we present a case of a 53-year-old man with superior vena cava (SVC) syndrome who developed LCNEC in the middle mediastinum. His chief complaint was facial edema. Chest X-ray revealed an abnormal shadow in the right upper mediastinum. Computed tomography (CT) scan of the chest revealed a 67-mm mass in the middle mediastinum. Tumor invasion caused constriction of the SVC. The patient underwent induction chemoradiotherapy with vinorelbin and cisplatin and concurrent radiation therapy. After induction therapy, the tumor size decreased remarkably and was resected completely. The pathological diagnosis was LCNEC.