We report a case of a 64-year-old man with pleomorphic carcinoma of the lung and thymic cyst. He was admitted to our hospital because of an abnormal shadow observed on chest X-ray. Computed tomography (CT) showed a mass lesion located in the right upper lobe and a non-invasive anterior mediastinal tumor adjacent to the left brachiocepharic vein. On enhanced CT, the lung mass showed central low-attenuation areas with a substantial enhancement in the periphery. Preoperative transbronchial blushing cytology of the mass revealed adenocarcinoma. With a diagnosis of primary lung cancer (cT3N0M0) and mediastinal tumor, an operation was performed through a median sternotomy. The mediastinal tumor was excised and a right upper lobectomy and were also accomplished, because the lung tumor did not show adhesion or pleural invasion. Histopathologic examination of the resected specimen revealed that the lung tumor composed of a mixture of spindle and giant cell features and contained a component of adenocarcinoma and squamous cell carcinoma. This finding yielded a pathological diagnosis of pleomorphic carcinoma (pT2N0M0). The mediastinal tumor was diagnosed as thymic cyst. The postoperative course was uneventful, and he is currently well 6 months after surgery.