Purpose: To analyze the correlation between acute and late injury in 973 prostate cancer patients treated with radiotherapy and to evaluate the effect of patient-, tumor-, and treatment-related variables on toxicity. Methods and Materials: Of the 973 patients, 542 and 431 received definitive or postprostatectomy radiotherapy, respectively. Three-dimensional conformal radiotherapy included a six-field technique and two-dynamic arc therapy. Toxicity was classified according to the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria. The correlation between acute and late toxicity (incidence and severity) was assessed. Results: Multivariate analysis showed that age <= 65 years (p=.06) and use of the three-dimensional, six-field technique (p<0001) correlated significantly with greater acute rectal toxicity. The three-dimensional, six-field technique (p=.0002), dose >70 Gy (p=.014), and radiotherapy duration (p=.05) correlated with greater acute urinary toxicity. Acute rectal toxicity (p<.0001) was the only factor that correlated with late rectal injury on multivariate analysis. Late urinary toxicity correlated with acute urinary events (p<.0001) and was inversely related to the use of salvage radiotherapy (p=.018). A highly significant correlation was found between the incidence of acute and late events for both rectal (p<.001) and urinary (p<.001) reactions. The severity of acute toxicity (Grade 2 or greater) was predictive for the severity of late toxicity for both rectal and urinary events (p<.001). Conclusion: The results of our study have shown that the risk of acute reactions depends on both patient-related (age) and treatment-related (dose, technique) factors. Acute toxicity was an independent significant predictor of late toxicity. These findings might help to predict and prevent late radiotherapy-induced complications. (C) 2010 Elsevier Inc.