A 79-year-old man, who had an occupational history of handling rushes (which were treated with pigmented earth containing 25% silica) for 30 years and a past history, eight years earlier, of primary pulmonary adenocarcinoma in the left lower lung (T2N2M0), was admitted to our hospital for the investigation of two nodular shadows in the right upper S3 which showed a double lesion detected on chest CT. A histological diagnosis of pulmonary adenocarcinoma was obtained by bronchoscopic examination, and so he was transferred to the Department of Thoracic Surgery and video-assisted thoracoscopic surgery (VATS) was performed. Subsequently, the large part of the tumor, in the central region, was diagnosed as a pulmonary adenocarcinoma, and the smaller part of the tumor, in the peripheral region, was found to consist of an adhesion of small nodules composed of pneumoconiosis due to the rushes. Multiple small nodules consisting of rush pneumoconiosis were histologically recognized surrounding this smaller part of the tumor. Although, at admission, we first suspected the presence of multicentric, metastatic lung cancer and an inflammatory tumor, the patient's occupational history also proved to be important, and we could not decide on the appropriate diagnosis before VATS because multiple small nodules consisting of rush pneumoconiosis overlapped the tumor.