In patients with complete double renal system with the involvement of only one system, there are several surgical alternatives for its resolution. Uretero-ureteral anastomosis has been presented as a good alternative, even in cases with atrophy of the affected system., Objective: To report our experience in patients with complete double renal system with only one system affected, with the surgical technique of uretero-ureteral anastomosis., Patients and Method: Retrospective study of patients with double renal system with involvement of one of the systems, treated with uretero-ureteral anastomosis technique between January 2015 and May 2022. The variables of age, specific pathology of the affected system, preoperative study, days of hospitalization, postoperative complications (leakage, obstruction, infection), and follow-up time were evaluated., Results: We analyzed 26 procedures in 25 patients, mean age 36.8 months (range: 8-80); 53.8% had ectopic ureter, 23% ureterocele, 11.5% sphincteric ureterocele, and 11.5% VUR of the lower system. All were studied preoperatively with urethrocystography and 65% with scintigraphy. 50% of the operated systems showed signs of renal atrophy. The average hospital stay was 2.2 days (range: 1-7). In an average follow-up of 26.5 months (range: 3-77), one patient presented leakage, no patient presented signs suggestive of obstruction, and one patient presented febrile urinary tract infection with persistent lower-grade reflux., Conclusion: In our experience, the uretero-ureteral anastomosis technique proved to be an easy and safe alternative to reproduce, with a success rate of 96%, 11% of grade I complications, and 4% of grade II complications according to the Clavien-Dindo classification.