This report deals with the macroscopic and microscopic histopathological findings of the upper urinary tract following a unilateral ureteroneocystostomy (UNC) in dogs. Both sides, operated and unoperated, were examined. The area of antireflux surgery was of particular significance. The decrease of flow which was always present on the operated side was caused by submucosal oedema of the bladder and not by the fatty tissue deposited intramurally or by the bladder muscle itself. The morphological findings were less pronounced than was to be expected following the significant obstruction on the operated side caused by anti-reflux surgery (ARS) and shown by the flow measurement and the sequential findings on scintigraphy.