Objective.The authors previously successfully applied the "flap-and-trough" (FT) method of antireflux ureterointestinal anastomosis (UIA) in a pilot set of 81 patients. This randomized prospective trial tested the effectiveness of this method in protecting the upper urinary tract from obstruction, reflux and infections. Material and methods. Forty-nine patients indicated for cystectomy and intestinal urinary diversion were randomly split into two groups, A and B. The FT antireflux UIA was applied in group A (n = 20), and refluxing direct elliptical UIA in group B (n = 29). Both groups were divided into two subcategories according to the type of diversion used: Ar (n = 10) and Br (n = 16) with low-pressure reservoirs and Ac (n = 10) and Bc (n = 13) with conduits. The follow-up evaluation compared the groups regarding perioperative complications, antireflux efficiency of FT, occurrence of obstruction and urinary infection, kidney morphology and glomerular filtration rate. Results.During the follow-up period (median 31 months), the obstruction occurred only in group Br (insignificant difference compared to Ar). A significant decrease in glomerular filtration rate and shortening of the left kidney occurred in group Br during the period and in comparison with Ar. There were no other considerable divergences in other studied parameters. Conclusions.The antireflux FT anastomosis represents a low risk for stenosis. The reduced occurrence of obstructive complications in comparison with direct UIA was statistically insignificant. Its construction did not increase the frequency of complications; on the contrary, it guarantees a better protection of renal morphology and function.