Background: Adding UGT1A1-guided irinotecan to capecitabine-based neoadjuvant chemoradiotherapy (CRT) significantly increased the pathological complete response (pCR) rate nearly doubling [J Clin Oncol. 2020 Dec 20;38(36):4231-4239]. Here, results of long-term outcome are reported. Methods: Eligible patients with clinical stage II/III rectal adenocarcinoma, UGT1A1 genotype *1*1 or *1*28 were randomized to the control group: pelvic radiation of 50 Gy/25 fractions with concurrent capecitabine, followed by a cycle of oxaliplatin and capecitabine; or the experimental group: radiation with capecitabine combined with weekly irinotecan 80 mg/m2 for patients with *1*1 or 65 mg/m2 for patients with *1*28, followed by a cycle of irinotecan and capecitabine. Surgery was scheduled for 8 weeks after completion of CRT. Five cycles of adjuvant XELOX chemotherapy were administered regardless of the pathologic result. Patients were stratified by UGT1A1genotype (*1*1 vs. *1*28) clinical T stage (cT3 vs. cT4) and tumor distance from the anal verge (≤5 cm vs. > 5 cm). The primary end point of pCR was reached. Survival time was calculated from the date of randomization to the date of event or the last follow-up. Secondary endpoints were defined as local failure for local control (LC), tumor recurrence or death from any cause for disease-free survival (DFS), and death from any cause for overall survival (OS). Results: Of the 360 patients initially enrolled, 356 were evaluated as the modified intention-to-treat population (n = 178 in both groups). A total of 311 patients underwent surgery and pCR was achieved in 80 patients, another 10 patients undergo a watch-and-wait approach after achieving cCR. With a median follow-up time of 48 months (Q25-Q75, 41-55 months), 57 deaths (33 and 24), 17 local failures (11 and 6) and 69 distant metastases (37 and 32) were observed, respectively. Overall, the 4y LC rate were 93% and 96% in control and experimental groups, with estimated LC HR of 0.53 (95% confidence interval [CI], 0.20-1.43), the 4y DFS rates were 69% and 74% (HR = 0.74, 95% CI 0.49-1.10), and the 4y OS were 80% and 85%, (HR = 0.70, 95% CI 0.42-1.19), respectively. In the subgroup analysis, irinotecan showed a significant improvement in DFS (HR = 0.77, 95% CI 0.61-0.98) and OS (HR = 0.71, 95% CI 0.51-0.98) in UGT1A1*1*1 patients. Conclusions: The addition of irinotecan to standard capecitabine-based CRT had a tendency towards improving LC, DFS, and OS, but without reaching statistical significance. UGT1A1*1*1 patients seem to benefit the most from irinotecan. Molecular studies and subsequent therapies should be considered. Clinical trial information: NCT02605265