Background and Clinical Significance: Retroperitoneal urinomas are uncommon complications that can arise following trauma, particularly in the context of congenital anomalies such as pyeloureteral duplication. These conditions pose significant diagnostic and therapeutic challenges, requiring a comprehensive and multidisciplinary approach to ensure optimal patient outcomes. Case Presentation: Here, we report the case of a 22-year-old male who presented to the emergency department with right lumbar and flank pain, nausea, and abrasions following a fall from a height. Initial imaging revealed a right-sided retroperitoneal urinoma and a rare congenital anomaly: complete pyeloureteral duplication with the upper pole draining into the right seminal vesicle. The patient underwent two surgical interventions, including the insertion of a ureteral stent and reimplantation of the ureter using a latero-terminal U trans U technique. Conclusions: This case highlights the complexity of managing traumatic retroperitoneal urinomas associated with congenital anomalies such as complete pyeloureteral duplication. It emphasizes the importance of timely surgical intervention to prevent complications and improve patient outcomes.