A 73-year-old man presented to the emergency department with the acute onset of severe lower abdominal pain. He recalled eating yellowtail fish the day before the onset of the pain. His temperature was 38°C, blood pressure 122/69 mm Hg, and heart rate 77 beats per minute. On physical examination, he had tenderness across the lower abdomen with rebound tenderness. Laboratory tests showed a white-cell count of 10,300 per cubic millimeter (reference range, 3300 to 8600) with 83% neutrophils. Computed tomography of the abdomen revealed a thickened gut wall and penetration of the small intestine by a linear, high-density body (Panel A). Laparotomy revealed a small-bowel perforation from a fish bone 2 cm in length (Panel B). Small-bowel resection was performed, and the patient received treatment with antibiotic agents. The postoperative course was uncomplicated, and the patient was discharged home on day 8 after surgery.