To identify prognostic factors associated with chronic renal insufficiency in children with posterior urethral valves (PUV), 22 children with PUV were submitted to a systematic protocol and prospectively followed. Prognostic factors associated with fetal echography and clinical and laboratory findings were studied on admission. Median follow-up was 76 months. The analysis was conducted in two steps: in univariate analysis, variables associated with adverse outcome were identified by the Kaplan-Meier method. The variables that were significantly associated with adverse outcome were then included in a multivariate analysis using the Cox model. Eleven patients (50%) developed chronic renal failure (CRF) during follow-up. After adjustment by the multivariate model, four factors were identified as independent predictors of adverse outcome: oligohydramnios (relative risk [RR] = 10.6, 95% CI = 2.7 - 77, P = 0.02), ventilatory support (RR = 6, 95% CI = 2 - 24, P = 0.01), urea higher than 40 mg/dl (RR = 3.7, 95% CI = 0.92 - 15.0, P = 0.06), and bilateral vesicoureteral reflux (VUR) (RR = 6.1, 95% CI = 1.25 - 30, P = 0.02). On the other hand, the presence of unilateral VUR was a protective factor against the development of CRF or death during follow-up (RR = 0.92, 95% CI = 0.87 - 0.98, P = 0.05).