A 45-year-old man referred to our hospital complaining of dry cough. Chest X-ray and CT scan film indicated tumor shadow in the right anterior mediastinum. Although preoperative diagnosis was teratoma, the specimen extirpated by thoracotomy revealed macroscopically and microscopically foreign body granuloma originated from gauzes. He had undergone segmentectomy of right upper lobe for tuberculosis 28 years ago, so the gauzes were thought to be left in right thoracic cavity at the operation. The foreign body granuloma originated from gauzes are iatrogenic and few cases were reported previously, however, whirl like pattern demonstrated by MRI is retrospectively considered to be an important diagnostic finding in this case.