Gossypibomas from inflammatory reactions to textile foreign bodies are a rare postoperative complication and are easily confused with neoplastic processes because of their diversity of symptoms and radiographic signs. Positron emission tomography (PET) is seldom used to diagnose gossypibomas and PET findings can result in false positives for a diagnosis of neoplastic disease. We describe the case of a 56-year-old man in whom PET findings showed an intrathoracic mass suggesting a tumor. The final diagnosis was gossypiboma, identified 23 years after pneumothorax surgery.