BACKGROUND: To evaluate and compare the survivals and radiotherapy-induced adverse events (AEs) of intensity-modulated radiotherapy (IMRT) with androgen deprivation therapy (ADT) and trimodality therapy, including low-dose iodine-125 brachytherapy, external beam radiotherapy, and ADT, for high-risk localized prostate cancer (LPC). METHODS: High-risk patients with LPC at T stage ≥ 3a, Gleason score ≥ 8, and initial prostate-specific antigen ≥ 20.0 ng/mL treated between 2010 and 2021 were retrospectively evaluated. All the patients were treated with IMRT plus ADT or trimodality therapy. In both groups, ADT was initiated 6 months before and continued for 2 years after radiotherapy. Survival and acute and late radiation-induced AEs were evaluated and compared. RESULTS: Two hundred and thirty-eight patients were treated with IMRT, and 91 underwent trimodality. Five- and 7-year biochemical-clinical failure-free survival (BCFFS) rates in the IMRT/trimodality group were 94.9/96.2, and 91.8/91.5%, respectively ( CONCLUSION: Treatment results of both IMRT and trimodality were considered to be good, and our results also indicated that the long-term survival of unfavorable high-risk patients with LPC who had three risk factors was poor in the IMRT group. Further treatment experience of both modalities must be accumulated with more appropriate patient allocations.