Between 1978 and 1993, 776 patients with lung cancer and 18 patients with chondromatous hamartoma were operated on in the department of Surgery II in Okayama University Hospital. 3 patients had both lung cancers and chondromatous hamartomas. They were all men. Two patients were 65 years old and the other was 82 years old. They all pointed out them by a medical examination of chest X-ray. 2 patients had lung cancers and chondromatous hamartomas in the same lobe, the other had them in other lobe of the same side. Lung cancer and chondromatous hamartoma localized in near area. It was difficult to discriminate chondromatous hamartoma between pulmonary metastasis of lung cancer before an operation.