Background: RTOG 0126 is a phase III trial for localized prostate cancer (PC) testing whether dose escalation to 79.2Gy with 3DCRT or IMRT will improve overall survival (OS). Methods: Stage cT1b-T2b with Gleason Score (GS) 2-6 and PSA ≥ 10 and <20 or GS 7 and PSA <15 were eligible and randomized to receive 79.2Gy or 70.2Gy. No androgen withdrawal was used. Treatment was 3DCRT or IMRT to 79.2Gy in 44 fractions or 70.2Gy in 39 fractions. The objective was to detect a 23% reduction in mortality hazard (HR=0.77) for 79.2Gy. ASTRO and Phoenix definition was used for biochemical failure (BF). Time to local progression (LP), distant metastases (DM), PC death, and late GI/GU toxicity was calculated from date of registration. OS was estimated by Kaplan Meier and arms compared with log rank test. BF, LP, DM, time to late GI/GU, and PC death were estimated by cumulative incidence method and arms compared with Gray’s test. Results: 1,532 men were randomized, 763 to 79.2Gy and 769 to 70.2Gy. 1,499 were eligible, 751 and 748 in the 79.2Gy and 70.2Gy arms respectively. Median age was 69, 70% had PSA < 10 ng/ml, 84% with GS 7, 57% had T1 disease, and 66% used 3D-CRT. With a median of 7.0 years follow up, the 5 and 10-yr rates of OS are 88% and 67% with 79.2Gy and 89% and 66% with 70.2Gy (p=0.87; HR (95%CI)=0.98 (0.79,1.21)). The ASTRO (Phoenix) BF rates at 5 and 10 yr are 25% (16%) and 30% (26%) with 79.2Gy and 40% (21%) and 45% (43%) with 70.2Gy (both p<0.0001). The 5 and 10-yr rates of LP are 1% and 4% with 79.2Gy and 2% and 8% with 70.2Gy (p=0.0059; HR (95%CI)=0.46 (0.27,0.81)). The 5 and 10 yr rates of DM are 2% and 5% with 79.2Gy and 3% and 8% with 70.2Gy (p=0.026; HR (95%CI)=0.57 (0.35,0.94)). The high dose arm had lower rate of salvage therapy, 13.5% vs 21%, p=0.0002. The 10 yr rates for time to late grade ≥ 2 GI/GU are 22%/15% with 79.2Gy and 16%/10% with 70.2Gy (p=0.0063/p=0.001). Time to late grade ≥ 3 GI was higher for the 79.2Gy arm (p=0.035) but time to late grade ≥ 3 GU toxicity was not (p=0.14). Conclusions: Despite significant improvement in BF, DM, and LP rates, dose escalation did not improve OS. Patients receiving high dose radiation experience more late toxicity. Clinical trial information: NCT00033631.