Adenocarcinoid of the appendix is an infrequent tumor with histologic features of both adenocarcinoma and carcinoid tumor. Although its malignant potential remains unclear, adenocarcinoids seem to be biologically more aggressive than conventional carcinoids. The aim of this study was to analyze long-term results of surgical treatment for appendiceal adenocarcinoid. A retrospective review (1991-2003) identified seven patients (median age 72, range 27-81 years) treated for appendiceal adenocarcinoid. The clinical data of these patients were reviewed. Follow-up was complete for all patients (median 60 months, range 24-108 months). Most cases presented with associated acute appendicitis (71%). First intention surgery consisted of appendectomy (m = 6) and right hemicolectomy (m = 1). In three patients, additional surgical procedures were performed (right colectomy). Indications for colectomy were tumor size (three cases) associated with appendectomy margin invasion in one case. One patient with lymph node and peritoneal involvement experienced recurrence 9 months after hemicolectomy and died of the disease at 2 years. One patient subsequently died of colon carcinoma 6 years after adenocarcinoid treatment. Five patients were alive without disease at the time of the last follow-up. Synchronous or metachronous colon carcinomas developed in three patients (43%). Our results suggest that appendectomy alone could be used for appendiceal adenocarcinoid provided that the tumor (1) is less than 1 cm; (2) does not extend beyond the appendix adventitia; (3) has less than 2 mitoses/10 high power fields; and (4) has surgical margins that are tumor free. Otherwise, carcinologic right colectomy seems to be indicated. The risk for developing colorectal adenocarcinoma seems to be extremely high in patients treated for appendiceal adenocarcinoid and warrants close follow-up with colonoscopic screening.