Radionuclide investigation of the kidneys and the urinary tract in children makes it possible to measure separate renal function, detect renal scars, visualize vesico-ureteric reflux and determine whether dilatation of the upper urinary tract is due to obstructive uropathy or not. Not all congenital anomalies of the urinary tract require surgery, and it is thus important to identify kidneys at risk by assessing the functional state of each kidney separately. Radiological examinations and sonography provide predominantly anatomic information, whereas the function of the kidneys and upper urinary tract can be reliably studied by scintigraphy. These functional data are essential when deciding on the most appropriate treatment for children with congenital urinary tract disorders.