To evaluate long-term freedom from biochemical relapse (FFbR) and overall survival (OS) after single-dose high-dose-rate brachytherapy (HDR-BT) compared with 2 or 3 fraction schedules. HDR-BT, delivering 1 × 19 Gy or 1 × 20 Gy (A = 49), 2 × 13 Gy (B = 138) or 3 × 10.5 Gy (C = 106), was given to patients with intermediate or high-risk prostate cancer as their sole treatment. Patients were staged with pelvic MRI and isotope bone scan. Transperineal transrectal ultrasound guided implantation was followed by MRI based CTV definition based on GEC ESTRO guidelines. Biochemical relapse was assessed using the Phœnix definition (PSA nadir plus 2 µg/L). Patients were evaluated prospectively from 6 months after implant and bi-annually thereafter. Estimates of freedom from biochemical relapse, and overall survival (OS) were calculated using the Kaplan-Meier (K-M) method and the log-rank test to test for significance. Univariate and multivariate hazard ratios (HR) were obtained using Cox's proportional hazard model. For multivariate modelling a stepwise reduction method was used. Median follow-up was 123, 116 and 120 months (p = 0.4), (A, B, C, respectively). Neo-adjuvant and adjuvant androgen deprivation treatment was given to 80% of all patients, median duration was 9 months for A and 6 months for B and C. K-M estimates of FFbR, at 8 and 10 years, were 67% and 64% (Group A), 78% and 72% (Group B), and 80% and 76% (Group C). Differences in FFbR between dose groups was not significant (p = 0.2). Similarly, no significant difference was seen in OS. Eight and 10-year estimates were 81% and 75% (A), 85% and 74% (B), and 90% and 83% (C); p = 0.5. Hazard Ratios for risk of biochemical recurrence were significant for ADT administration (yes/no) and overall risk category, in multivariate analyses. Only the latter was significant in univariate analysis for risk of death, Gleason risk (low, intermediate, high), MRI tumor stage risk and overall risk category were significant in univariate analyses. Only tumor stage and Gleason risk were significant in multivariate analyses. Concerns around the efficacy of 19-20 Gy single dose HDR BT as monotherapy, based on early data, may have been unfounded. Long-term outcome data up to 10 years show no significant difference in PSA control and overall survival compared to 2 and 3 fractions of HDR-BT.