Guidelines and standards supplementing the German "Röntgenverordnung" initiated a complex system of quality control in diagnostic radiology. Cost and profit are analysed for two hospitals of comparable size (Klinikum Buch and Klinikum Nürberg). The considerable expenses that must be incurred for measuring devices, equipment, working time and extra charges on the one hand, are the items that are opposed to achieving a higher image quality and dose reduction on the other. Public quality control enables to demonstrate the quality and to optimise imaging procedures in diagnostic radiology. A critical evaluation of the results of quality control suggests further developments. We should consider larger time intervals for quality tests in some cases, while focussing on techniques with high radiation exposure, e.g. computed tomography, where dose reductions are highly effective.