Small bowel perforation by a fish bone is unusual, and the preoperative diagnosis is difficult. We report a 91-year-old man who had a sudden onset of upper abdominal pain with muscle guarding after a meal. Computed tomography of the abdomen revealed a thickened ileum, and with suspicion of a metal foreign body in the intestine, together with multiple gallbladder stones and cholecystitis. Also, intestinal perforation and pneumoperitoneum could not be ruled out. He had immediate surgical intervention and an ileal perforation caused by a fish bone with turbid ascites was diagnosed. A partial resection of the small intestine and cholecystectomy were performed. The patient’s hospital course was smooth and he was discharged home in good condition. An accurate diagnosis and emergency surgical intervention may have aided in the good results in this case.