Purpose - The optimal frequency of prostate cancer image guided radiation therapy (IGRT) has not yet been clearly identified. This study sought to compare the safety and efficacy of daily versus weekly IGRT. Materials and methods - This phase 3 randomized trial recruited patients with N0 localized prostate cancer. The total IGRT doses in the prostate ranged from 70 Gy to 80 Gy, sparing the lymph nodes. Patients were randomly assigned (1:1) to 2 prostate IGRT frequency groups: daily and weekly (ie, on days 1, 2, and 3 and then weekly). The primary outcome was 5-year recurrence-free survival. Secondary outcomes included overall survival and toxicity. Post hoc analyses included biochemical progression-free interval, clinical progression-free interval, and other cancer-free interval. Results - Between June 2007 and November 2012, 470 men from 21 centers were randomized into the 2 groups. Median follow-up was 4.1 years. There was no statistically significant difference in recurrence-free survival between the groups (hazard ratio [HR] = 0.81; P = .330). Overall survival was worse in the daily group than in the weekly group (HR = 2.12 [95% confidence interval (CI), 1.03-4.37]; P = .042). Acute rectal bleeding (grade ≥1) was significantly lower in the daily group (6%) (n = 14) than in the weekly group (11%) (n = 26) (P = .014). Late rectal toxicity (grade ≥1) was significantly lower in the daily group (HR = 0.71 [95% CI, 0.53-0.96]; P = .027). Biochemical progression-free interval (HR = 0.45 [95% CI, 0.25 - 0.80]; P = .007) and clinical progression-free interval (HR = 0.50 [95% CI, 0.24-1.02]; P = .057) were better in the daily group, whereas other cancer-free interval was worse in the daily group (HR = 2.21 [95% CI, 1.10-4.44]; P = .026). Conclusions - Compared with weekly control, daily IGRT control in prostate cancer significantly improves biochemical progression-free and clinical progression-free interval, and rectal toxicity.