BACKGROUND: Prostate cancer is most commonly diagnosed at a localized stage, allowing the majority of patients to receive curative treatment. The prognosis is often favorable, and there are numerous treatment options available, emphasizing the importance of assessing the side effects associated with each treatment. Low-dose-rate (LDR) brachytherapy is one such treatment option, supported by robust evidence regarding its efficacy and side effects. However, most published data primarily rely on physician-assessed toxicity, which may underestimate the patient's experience of side effects. This study aims to provide a comprehensive overview of the urinary side effects of LDR brachytherapy, with a focus on patient-reported outcomes. METHODS: This retrospective study included 199 patients treated with LDR-brachytherapy years 2000-2012 at Helsinki University Hospital. Questionnaires used to assess urinary toxicity were International Prostate Symptom Score (IPSS) and The Danish Prostatic Symptom Score (DAN-PSS). Additionally, sexual function was assessed using the International Index of Erectile Function (IIEF) questionnaire. Urinary function was assessed with flowmetry, reporting peak flow rate and postvoid residual measurement. RESULTS: There was a deterioration in urinary function during the first six months post-procedure, as evidenced by a decline in the urinary function questionnaires and uroflowmetry measurements. For most patients, this deterioration was transient, with median symptom scores returning to baseline after one year. A slight discrepancy was observed between patient-reported outcome measures and urinary function assessed by flowmetry. CONCLUSIONS: LDR brachytherapy is a well-tolerated treatment for localized prostate cancer. While many patients experience acute side effects that subside relatively quickly, there is a small risk of prolonged side effects. This risk should be thoroughly discussed with patients when making treatment decisions.