PURPOSE: Primary adenocarcinoma of the anus is a rare tumor. The current standard treatment consists of abdominoperineal resection (APR). The aim of this Rare Cancer Network study was to evaluate the prognostic factors and outcome after the three most commonly used treatment approaches. METHODS AND MATERIALS: This multicenter study collected data from 82 patients: 15 with T1 (18%), 34 with T2 (42%), 22 with T3 (27%), and 11 with T4 (13%) tumors according to the TNM classification (International Union Against Cancer, 1997). Patients were separated into, and analyzed according to, three treatment categories: radiotherapy/surgery (RT/S group, n = 45), combined radiochemotherapy (RT/CHT group, n = 31), and APR alone (APR group, n = 6). The main patient characteristics were evenly distributed among the three groups. RESULTS: The actuarial locoregional relapse rate at 5 years was 37%, 36%, and 20%, respectively, in the RT/S, RT/CHT, and APR groups (RT/S vs. RT/CHT, p = 0.93; RT/CH vs. APR, p = 0.78). The 3-, 5-, and 10-year overall survival rate was 47%, 29%, and 23% in the RT/S group, 75%, 58%, and 39% in the RT/CHT group, and 42%, 21%, and 21% in the APR group (RT/CHT vs. RT/S, p = 0.027), respectively. The 5- and 10-year disease-free survival rate was 25% and 18% in the RT/S group, 54% and 20% in the RT/CHT group, and 22% and 22% in the APR group (RT/CHT vs. RT/S, p = 0.038), respectively. Multivariate analysis revealed four independent prognostic factors for survival: T stage, N stage, histologic grade, and treatment modality. CONCLUSION: Primary adenocarcinoma of the anal canal requires rigorous management. Multivariate analysis showed that T and N stage, histologic grade, and treatment modality are independent prognostic factors for survival. We observed better survival rates after combined RT/CHT. We also recommend using APR only for salvage treatment.