The early detection of urologic abnormalities by antenatal sonography has resulted in the investigation of many infants and neonates for suspicion of either obstructive uropathy or reflux nephropathy. Nuclear medicine techniques allow to assess renal parenchyma integrity, to detect pyelonephritic scars and to measure absolute and relative renal function; these methods are easy to perform and reproducible, without any sedation, repeated venous punctures or bladder catheterization. Furthermore, the use of dynamic tubular tracers and frusemide test is a very usefull method which can differentiate between upper and/or lower urinary tract obstruction and determine the degree of obstruction (severe or incomplete) in order to plan for surgery or conservative treatment. The detection of vesicoureteric reflux may be difficult as it is an intermittent phenomenon: the use of the indirect radionuclide cystography (IRC), that is to say after completion of a dynamic renography, allows to detect reflux with a high sensitivity because images can be recorded continuously until the child voids, without any bladder catheterization and at low radiation dosis. In case of discordant results between micturating cysto-urethrography and IRC or of concomittant obstructive uropathy, the direct radionuclide cystography (DRC) is indicated for appropriate treatment. Nuclear medicine techniques do not give morphological information about the urinary tract and should be considered as complementary to radiological investigations in first evaluation of children with recurrent urinary tract infections or hydronephrosis.