After diagnosis of posterior urethral valves, children will be randomised either to antibioprophylaxis alone or antibioprophylaxis plus circumcision. Circumcision will be performed at the time of valve resection. Children will undergo a cystogram between 1 and 4 months to control valve resection. They will be followed for two years and the number of febrile UTIs in each group will be compared. The diagnosis of febrile UTI will be confirmed by urethral catheterisation or suprapubic aspiration. A DMSA scan will be performed at the beginning and end of the study to determine whether children who have presented febrile UTIs show deterioration of their DMSA as compared to those who did not present febrile UTIs.