Background: To assess the effect of the timing of biochemical failure (bF) after definitive radiotherapy with external beam (EBRT) or low dose-rate brachytherapy (LDR) on clinical failure (cF) and prostate cancer-specific mortality (PCSM). Methods: From 1996 to 2009, 4478 patients were treated and by 2010, 456 patients were noted to have a bF. They were categorized as early (< 5 years post-therapy) or late (≥ 5 years post-therapy) failures. Factors thought to influence cF and PCSM were scored. Cox regression was used to assess the timing of bF on cF and Fine and Gray regression was used to assess the timing of bF on PCSM. Results: There were 330 (72.4 %) patients categorized as early and 126 (27.6 %) as late failures. The median PSA follow-up post-radiotherapy for the early bF group is 82 months vs. 155 months for the late bF group, and the median PSA follow-up post-bF is 54 months for the early bF group vs. 69 months for the late bF group. The early failures were more likely to be high-risk (p = 0.0080), have a higher Gleason score (p = 0.0008), and use ADT (p = 0.0325). The five-year rate of cF post early bF is 61% vs 43% post late bF (p <0.0001). The five-year rate of PCSM post early bF is 27% vs 9% post late bF (p <0.0001). The multivariable analyses assessing the cF and PCSM are shown in Table. Conclusions: Early bF is associated with higher rates of cF and PCSM. Patients treated with LDR have a lower risk of PCSM.