Background: The aim if this single institute UK-based study was to look at 3-year and 5-year bRFS and toxicity profiles. Methods: It is a prospective data study with a total number of 174 patients who were treated with single-fraction HDR monotherapy between July 2014 and February 2017. Biochemical recurrence is defined using Phoenix criteria. Results: The median age was 67.5 years with the median presenting PSA of 8. Majority of patients were lower risk group with 55% for combined low and favourable intermediate risks. 81 patients had Gleason score 6(3+3) and 77 patients had GS 7(3+4). Total hormone duration was 8 months and median duration of hormone prior to HDR monotherapy was 4 months. Overall bRFS at 3 years was 96% and 5 years was 88%. 5-year bRFS as per risk stratification was 100% in low risk, 92% in favourable intermediate risk, 83% in unfavourable intermediate risk and 79% in high-risk groups. This study had better 5-year overall bRFS compared to published data in single fraction HDR monotherapy (88% vs 73.5%, p value 0.001) (Morton et al., 2020). Despite inferior 5-year overall bRFS in compared to 2-fractionated HDR monotherapy (88% vs 95%) (p value 0.001), no difference in 5-year bRFS noted in low and favourable intermediate risk groups (100% vs 100% and 92% vs 93% respectively) (Morton et al., 2020). Two-thirds (71%) of biochemically recurred patients found to have local recurrence disease. The median time of biochemical recurrence was 47 months. Higher risk groups had higher 5-year biochemical recurrence risk. Acute and late toxicity profiles were minimum with acute G2 GU toxicity (2%) and GI toxicity (1%); late G2 GU toxicity (2%) and GI toxicity (0%) with no G3, G4 GU or GI toxicities. Conclusions: This prospective study had shown better overall 5-year bRFS especially in low and favourable intermediate risk groups with minimal toxicities. Therefore, single-fraction HDR monotherapy could be considered for elderly or patients with significant co-morbidities who are more suitable for single treatment rather than 2 fractions in these risk groups. Further randomised multicentre studies in these risk groups are suggested.