Objective: Adenomyoma is a term generally applied to nodular lesions showing proliferation of both epithelial and smooth muscle components. It is usually presented as biliary obstruction. Most cases are misdiagnosed as adenoma or carcinoma by preoperative endoscopic or radiologic. Therefore, it is frequently treated with extensive surgery. Method: We report a case of a 28 year-old man with an adenomyoma located in the ampulla of vater diagnosed by endoscopic piecemeal resection. Results: On histologic examination, the lesion consisted of hyperplastic glandular lobules, mainly located in the muscle layers of the vaterian system. The lobular formations consist of small glands surrounded by myofifroblastic, fibroblastic proliferation, sparse capillaries and inflammatory cells. IHC: Ki67: rare cells with a positive nuclear staining were presenting in the epithelial and mesenchymal components AML: The myofibroblastic of most spindle cells was confirmed by a strong cytoplasmic expression. Conclusion: Real incidence of adenomyoma of the vaterian system is difficult to appreciate as different names (adenomyoma, adenomyomatosis, myoepithelial hamartome) are used to designate the same histological lesion. Adenomyoma was diagnosed only in adult patients -mean age: 63 y). The histogenesis is still a subject of controversy. The most widely accepted hypothesis is that the lesion may represent a form of incomplete heterotopic pancreas.