PURPOSE: Boys with posterior urethral valves (PUV) have increased risks of urinary tract infection (UTI) voiding dysfunction and ongoing renal damage. Circumcision has been shown epidemiologically to reduce UTIs, but no trial has yet confirmed this in PUV. Circumcision is not routinely performed in boys with PUV in our unit, but one quarter of our patients are circumcised for religious reasons. It may be hypothesized that circumcision reduces the risk of subsequent urinary tract infection in boys with PUV. This study aims to test this hypothesis by comparing the risk of UTI, and subsequent renal outcome, in PUV in uncircumcised boys with those who were circumcised. METHODS: A retrospective cross-sectional case note review of boys with PUV was performed, and the following were documented: age at presentation, method of diagnosis, method of treatment, initial renal status, and timing of treatment; use and timing of urinary tract diversion; timing of circumcision; and UTIs-date, organism, and treatment. RESULTS: Seventy-eight patients were identified, mean age 6.7 years (range, 1-18). These boys experienced 78 UTIs in the uncircumcised state. Subsequently, 27 were circumcised, experiencing 8 UTIs. Eighteen boys were diverted. The incidence of UTI was reduced from 0.50 +/- 0.14 (mean +/- SEM) UTIs annually uncircumcised to 0.09 +/- 0.02 (mean +/- SEM) circumcised (P <.01, Student's t test). CONCLUSION: In PUV, circumcision reduces the incidence of UTI by 83%, every circumcision prevents 1 UTI on average. Early circumcision in all PUV is beneficial, but a larger randomised control trial should be considered to confirm this.