Surgeons in Japan thought they were removing a tumor from a 49-year-old man who was suffering from abdominal pain in late May.
Instead, they found a 25-year-old surgical towel that had crumpled into what looked like a softball-shaped tumor, Agence France-Presse reported.
The patient apparently had been carrying the cloth since 1983, when surgeons left it in him after minor ulcer surgery.
He went to Asahi General Hospital in late May after suffering pain. Doctors, at the time, found what they believed to be an 8-centimeter tumor.
According to an Asahi General Hospital spokesman: "The towel was greenish-blue although we are not sure about its original color."