A 62-year-old male patient was admitted to our department with a purulent fistula at the site of previous surgery in the right posterolateral thoracic area. The fistula was painful, warm, and erythematous with induration and continuous milky purulent drainage. He had a past medical history of diabetes mellitus from 20 years ago, which was treated with insulin injections. He also had two previous surgeries, the first was right posterolateral thoracotomy and pneumonectomy for the management of chronic tuberculosis about 47 years ago, and the other one was abdomino-pelvic resection for the management of colorectal cancer. The patient had developed a purulent lesion from two years ago, but mentioned no other symptoms. He also mentioned that his diabetes mellitus was severe in these 2 years. On physical examination, he had a 3*3 cm lesion with purulent secretion in the right posterolateral thoracic area. The surrounding tissue was red and tender. Chest X-ray showed opacities covering the whole right hemithorax and radiopaque strip. The patient was investigated with a chest computed tomography (CT) scan without contrast, which showed a giant lesion within the right thoracic cavity with thread-like calcifications. With suspicion of gossypiboma, right video-assisted thoracoscopic surgery was planned. Preoperative lab testing showed a white blood cell count of 10,600/μL with 81.6% polymorphonuclear neutrophils and 7.9% lymphocytes. C-reactive protein was in the upper limit of normal. Other blood examinations were normal. Microbial examination of the lesion showed infection with E. coli, which was resistant to ceftriaxone and ampicillin sulbactam. An infected surgical sponge was detected in the surgery. Due to severe adhesion to thoracic structures and mediastinum, we had to convert the operation to a right posterolateral thoracotomy. And it was removed from the thoracic cavity without any complications. Along with the sponge, a considerable amount of blood and suppuration was also removed from the thoracic cavity. A chest tube was inserted to drain the remnant purulent material. We used a chest tube and feeding tube catheter to irrigate the pleural space with warm normal saline (1000 cc) three times/day. The postoperative irrigation continued until the chest tube fluid became clear, lab examination became normal, and the patient did not have any signs of fever and infection. The chest tube was removed 3 days after surgery. The patient was then discharged with no symptoms or complications.