OBJECTIVES: Amphicrine-type mixed adenoneuroendocrine carcinomas are exceedingly rare lesions of the gastrointestinal tract, comprising tumor cells simultaneously demonstrating both neuroendocrine and exocrine features. To date, only 14 cases of amphicrine carcinoma have been reported; here we report the first definitive case of amphicrine carcinoma in the small bowel. METHODS: A 72-year-old woman who sought treatment for nonspecific abdominal complaints was found to have a duodenojejunal junction tumor and underwent radical surgical resection. RESULTS: Morphologically, the tumor consisted of areas of moderately differentiated adenocarcinoma intermingled with areas characteristic of neuroendocrine tumor. The entire tumor showed strong, diffuse immunoreactivity for synaptophysin. Coexpression of exocrine and neuroendocrine features by neoplastic cells indicates bivalent differentiation, and therefore the tumor was classified as an amphicrine carcinoma of the small bowel. CONCLUSIONS: Demonstration of amphicrine carcinoma in the small bowel carries implications with regard to the common origin of exocrine and neuroendocrine cells in the gastrointestinal tract.