An 80-year-old man under treatment for respiratory insufficiency due to silicosis abruptly developed abdominal pain and tarry stool. The patient underwent laparotomy for a probable diagnosis of acute abdomen. At laparotomy, reddish and swollen serosa were found in four parts of the ileum. The small intestine including the lesions was resected. Histological diagnosis of the resected specimen with irregular shaped ulcers was polyarteritis nodosa (PN). Twenty-seven patients with PN of the small intestine, undergone laparotomy, have been reported in the Japanese literature, and only one of them had been diagnosed preoperatively. The prognosis of this disease is poor. Early diagnosis and early treatment with steroids and immunosuppresive agents are essential for better prognosis.