We report the results of the trend of the residual renal function (RRF) of 15 patients with serious forms of hind urethral valves (HUV) which agreed to be long term regularly controlled after surgical correction at the Children's Surgical Hospital of Bologna University. The nephrological follow-up started in 1985 is based on a periodical control at least once a year, of some indicatives parameters of the glomerulars activity (creatinine clearance according Schwartz and creatinine reciprocal), of the tubular activity (urinary flux ml/kg/h, per cent fraction of Na excretion) and the dynamical test of the RRF started in 1991. The results although the low cases studies, are not statistically significant, the Authors underline the validity of the adopted method. Although of the simplified and/or indirect type, this is able to give clinically reliable informations of the renal functionality evolution avoiding particularly complex or invasive analysis.