Introduction: Gossypiboma is defined as retained foreign object (sponge, needle, and instrument) in patient's corpus after operation that is recognized as a medical error. It may induce catastrophic implications for the patient and medical care providers. We present a case with a 17-year-old gossypiboma after cesarean section. Case Presentation: A 49-year-old woman was admitted to the outpatient clinic of Rasool-e-Akram hospital of Tehran, Iran, in 2016 presenting with abnormal uterine bleeding (AUB), abdominal pain, and urinary symptoms for many years. She underwent hysteroscopy. Operative findings included intrauterine synechiae and a polypoid lesion. Besides, a thread-like foreign body was observed in the anterior surface of the uterine cavity, which was suspected as a cesarean section suture material that was extracted. After hysteroscopy, uterine bleeding stopped although abdominal pain and urinary symptoms maintained. Voiding cystourethrogram (VCUG) and MRI revealed a mass between uterus and bladder. Then, laparotomy was performed. After opening the abdominal wall under general anesthesia, we explored internal organs and encountered a necrotic mass revealing an old organized gauze between bladder and uterus, which infiltrated the uterus and trigon. It was extracted and then, hysterectomy and bladder repair were carried out. Conclusions: Surgical sponges are the most common foreign materials retained in abdominal cavity.