Concomitant radiochemotherapy (RCT) is the standard for locally advanced anal canal carcinoma (LAACC). Questions regarding the role of induction chemotherapy (ICT) and a higher radiation dose in LAACC are pending. Our trial was designed to determine whether dose escalation of the radiation boost or two cycles of ICT before concomitant RCT lead to an improvement in colostomy-free survival (CFS). Patients with tumors ≥ 40 mm, or < 40 mm and N1-3M0 were randomly assigned to one of four treatment arms: (A) two ICT cycles (fluorouracil 800 mg/m(2)/d intravenous IV infusion, days 1 through 4 and 29 to 32; and cisplatin 80 mg/m(2) IV, on days 1 and 29), RCT (45 Gy in 25 fractions over 5 weeks, fluorouracil and cisplatin during weeks 1 and 5), and standard-dose boost (SD; 15 Gy); (B) two ICT cycles, RCT, and high-dose boost (HD; 20-25 Gy); (C): RCT and SD boost (reference arm); and (D) RCT and HD boost. Two hundred eighty-three of 307 patients achieved full treatment. With a median follow-up period of 50 months, the 5-year CFS rates were 69.6%, 82.4%, 77.1%, and 72.7% in arms A, B, C, and D, respectively. Considering the 2 × 2 factorial analysis, the 5-year CFS was 76.5% versus 75.0% (P = .37) in groups A and B versus C and D, respectively (ICT effect), and 73.7% versus 77.8% in groups A and C versus B and D, respectively (RT-dose effect; P = .067). Using CFS as our main end point, we did not find an advantage for either ICT or HD radiation boost in LAACC. Nevertheless, the results of the most treatment-intense arm B should prompt the design of further intensification studies.