4642 Background: The magnitude of the benefit of adding adjuvant hormonal treatment to radiotherapy for locally advanced prostate cancer is still unclear. We performed a pooled-analysis of phase III trials, to quantify the eventual benefit in recurrence decrease. Methods: All prospective phase III trials were considered eligible. A pooled analysis was accomplished, and event-based relative risk ratios (RR) with 95% confidence interval (CI) were derived through both a fixed- (FEM) and a random-effect model (REM) approach. Significant differences in primary outcome (recurrence rate), and secondary outcomes (overall survival), were explored. Magnitude outcome measures were: absolute benefits and number of patients needed to treat (NNT) for 1 patient to benefit. Heterogeneity test was applied as well. Results: Six trials designed to look if hormonal treatment plus radiotherapy decreases recurrence rate (3,571 patients) were gathered. In the primary outcome, the combined approach significantly improves the recurrence rate when applying the FEM (RR 0.72, 95% CI 0.68, 0.77, p < 0.0001), with an absolute benefit of 10.7%. The NNT was 9 patients. Although significant heterogeneity was found (p = 0.00001), the benefit remains significant at the REM as well (RR 0.67, 95% CI 0.54, 0.82, p < 0.0001). Although significant at FEM (RR 0.93, 95% CI 0.86, 1.00, p = 0.039) but heterogeneous (p = 0.0007), the overall survival demonstrated a not-significant trend in favour of the combined strategy at REM (RR 0.90, 95% CI 0.75, 1.10, p = 0.263). Conclusions: Considered all the available phase III trials, the combination of adjuvant hormonal treatment with radiotherapy over standard exclusive radiotherapy significantly decreases the recurrence rate in patients affected by localized prostate cancer. The significant heterogeneity in the analysis underscores the existing difference in patient’ characteristics. No significant benefit in overall survival was found. No significant financial relationships to disclose.