Purpose: To evaluate erectile function (EF) prospectively from 1 to 2 years post-brachytherapy in patients with a baseline IIEF5 score>16., Methods: Between 2007 and 2012, 179 patients underwent an exclusive brachytherapy for localised low risk prostate adenocarcinoma. Neo-adjuvant hormotherapy (15.6%) and post-brachytherapy intake phosphodiesterase inhibitors (PDE5i) were not considered as exclusion criteria. EF was evaluated via a scoring questionnaire IIEF5 before the surgical implantation, at month 12 and 24 post-operation. Only patients with an initial IIEF5 score>16 were included., Results: Of the 179 patients, 102 (57%) had a baseline IIEF5>16. At 12 months, 51.1% maintained an IIEF5>16 and 24.5% had a mild to moderate erectile dysfunction (ED), so that a total of 75.6% with IIEF5≥12. About 18% of patients had used PDE5i. At 24 months, 53.2% had an IIEF5>16 and 80.6% had an IIEF5≥12. Severe ED was reported in only 14.5% of the patients. The mean IIEF5 was 16.2 with an average decline of 5 points from the initial stage. All patients who were treated with PDE5i (27%) could have sexual intercourse. EF at baseline was reported as the only predictive factor of ED in multivariate analysis, 70% of patient without ED initially, had an IIEF5>16 at 1 and 2 years., Conclusion: Severe ED was quite rare (14%) during the first 2 years post-brachytherapy and more than half of patients maintained an IIEF5>16. The main predictive factor was the erectile function at baseline., Level of Evidence: 4., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)