A 23-year-old man was admitted for examination of an abnormal shadow in the right lower lung field. A chest CT scan revealed a nodule in the right lower lobe and a calcified nodule in the right upper lobe. A diagnosis of lung adenocarcinoma in the right lower lobe was made by transbronchial cytology. After resection of the right lower lobe and partial resection of the nodule in the right upper lobe were performed, we diagnosed lung adenocarcinoma in the right lower lobe (pathological stage IIIA) and hamartoma in the right upper lobe. Although several authors have reported cases of synchronous pulmonary hamartoma and lung cancer, it is uncommon in young patients. Since patients with hamartoma could also have lung carcinoma, careful observation is needed.