A 59-year-old Japanese man was incidentally discovered to have multiple polyps in the duodenum by endoscopy during a health checkup. Laboratory studies showed an elevated level of serum somatostatin. The mutation of the MEN1 gene was not observed. An endoscopic examination revealed multiple polypoid lesions in the bulbus and in the second portion of the duodenum. An upper gastrointestinal series also showed the multiple polypoid lesions in the bulbus, and in the descending and horizontal portions of the duodenum. The biopsy specimen showed small monotonous cells with round nuclei compatible with a carcinoid tumor. The tumor cells were positive for somatostatin and gastrin. Based on the clinical diagnosis of multiple carcinoids of the duodenum, a pancreas-sparing duodenectomy was performed. Macroscopic findings showed about 30 polypoid lesions throughout the duodenum. The biggest one was not over 10 mm in size. A histological examination revealed well-demarcated carcinoid tumors located in the submucosal layer. Immunohistochemically, the tumors were diffusely positive for somatostatin and were scatteringly positive for gastrin. The patient's postoperative course of treatment was uneventful and his postoperative serum somatostatin went down to normal range. The pancreas-sparing duodenectomy is a safe and effective treatment in patients with multiple carcinoids of the duodenum, that are smaller than 1 cm in size.