Background: Conservative-surgery (CS) brachytherapy (BT) techniques for local therapy in bladder-prostate rhabdomyosarcoma (BP-RMS) seeks to retain organ function. We report bladder function after high-dose-rate (HDR) BT combined with targeted CS for any vesical component of BP-RMS. Procedure: Prospective cohort of all BP-RMS patients between 2014-19 receiving HDR-BT (Iridium-192, 27.5Gy in 5 fractions) with/without percutaneous endoscopic-polypectomy (PEP) or partial cystectomy (PC). Functional assessment included frequency-volume-chart, voided volumes, post-void residual, flow studies, continence status and ultrasound scanning; abnormalities triggered video-urodynamics. Results: Thirteen patients (10 male), aged 9 months to 4 years (median 23 months), presented with localised fusion-negative embryonal BP-RMS measuring 23-140mm (median 43mm) in cranio-caudal extent. After induction chemotherapy, local treatment consisted of PC+BT in three, PEP+BT in four and BT alone in six. At a median 3½ years (range 1¾-7 years) follow up, all were alive without relapse. At a median age of 6 years (4-9 years), the median bladder capacity was 86% (47%-144%) of that expected for age, including 75% (74-114%) after PC. There was no relation to radiation dose to the bladder. Complications occurred in two: one urethral stricture and one vesical decompensation in a patient with pre-existing high-grade VUR. The remaining patients are dry by day; five with anticholinergic medication for urinary urgency. Three patients are enuretic. Conclusions: Day-time dryness at a median 3½ years after CS-HDR-BT was achieved in 92%, with 85% voiding urethrally, and 62% attaining day-and-night continence aged 4-9 years. We report reduced open surgery, with minimally-invasive percutaneous surgery with HDR-BT or brachytherapy alone being suitable for many.