Primary adenocarcinoma of the appendix is a rare malignancy that constitutes less than 0.5% of all gastrointestinal neoplasms. Usually the diagnosis is made only after histological examination of surgically removed inflamed appendix. Alternatively represent an unexpected finding, confirmed by frozen section, during surgery performed for acute appendicitis or other non appendiceal pathologies. Natural history is strongly influenced by anatomic peculiarities of the appendix that predispose to early spread and perforation. Frequently is associated with synchronous and metachronous colorectal or extraintestinal cancers. The correct management is the right hemicolectomy as a primary procedure in the case of preoperatively or intraoperatively diagnosis or as secondary procedure, after two-three weeks from appendectomy, when the microscopic examination of specimen reveals the presence of adenocarcinoma. Right hemicolectomy is the best treatment for all histologic types (colonic, mucinous, adenocarcinoid), in presence of perforation and even in Dukes A tumors. A careful intraoperative search for synchronous lesions and a life-long program of surveillance for the detection of early stage metachronous carcinomas are recommended. The Authors report a case of primary adenocarcinoma of the appendix occurred in a 78 year-old female patient, diagnosed incidentally during surgery performed for ileus from suspected cecal neoplasm.