Twenty-one cases of posterior urethral valves experienced in the last 26 years were reported with special references to the morphological and functional sequelae of the upper and lower urinary tracts after the valve ablation. Furthermore, several problems, such as transient urinary diversion, vesicoureteral reflux (VUR), lower ureteral obstruction, transurethral valve ablation, bladder function and renal insufficiency, were also discussed. The age at the first examination ranged from 0 day to 13 years. Eight boys were first examined under one year of age. Although the most frequent complaint was urinary infection, some characteristic features were observed in each age group. In all of the children the valves were classified as type I (Young). Seven children had severe ones. Endoscopic examination was thought to be essential to find mild ones. VUR was found in 16 children (28 ureters). Grade IV was encountered most frequently (13 ureters) with prominent laterality to the left side. The severity of the renal scar paralleled to the grade of VUR. Most of the dwarf kidneys were thought to be hypodysplastic. Valve ablation was performed immediately after the diagnosis in 17 of the 21 children. Eight children were under one year of age when their valves were ablated. As a principle, VUR was followed conservatively after the valve ablation. VUR highly tended to disappear or improve when it was of low grade or valve ablation was performed under one year of age. However, when the ureteral orifices were disappearance of VUR was rare and recovery of renal function was not observed. In 5 children antireflux surgery was added. Although a dilated upper urinary tract without VUR was found in 2 children (2 ureters), it disappeared promptly after the valve ablation.(ABSTRACT TRUNCATED AT 250 WORDS)