We report on a case of gossypiboma. A 78-year-old man was admitted to our hospital with acute abdomen. He had undergone an operation for colon cancer 4 mo previously. Abdominal ultrasonography revealed an echogenic lesion with a hypoechoic rim and strong posterior acoustic shadowing in the lower abdomen. Diagnosis of gossypiboma can be made by ultrasonography to avoid loss-of-chance of survival. We reviewed the English literature briefly of gossypiboma from the medical and juridical view. According to the theory of loss-of-chance, the damage of plaintiff is the loss of the chance of survival or recovery, rather than the final harm. The victim would allow recovery for the loss of the chance from the defendant. But the plaintiff would show by a preponderance that he was deprived of a better chance of a cure. Under the proposed rule, the compensable value of the victim would be the plaintiff's compensation for the loss of the victim's chance of survival.