We report herein the unusual case of a 45-year-old Japanese man whose chest X-rays revealed an abnormal shadow, increasing in size. A chest wall tumor was suspected, based on the findings of computed tomography (CT) of the thorax, the CT number of which was -137, chest roentgenogram, and an echograph. An open biopsy was performed to establish the final diagnosis. The resected tumor was a pedunculated pleural mass, yellowish in color, the pathological diagnosis of which confirmed a lipoma. Intrathoracic lipomas are rare, but pleural lipomas are seen even less frequently. CT, echography, and percutaneous needle biopsy have been found useful for diagnosing intrathoracic lipomas, but these examinations are not always adequate for confirming the final diagnosis. Consequently, tumor resection is essential for obtaining a pathological diagnosis.