Application of the general principles of radiation protection to medical diagnostic radiology implies that each procedure using X rays or radionuclides is to be justified and optimised. Optimisation in diagnostic radiology implies that the radiation burden to the patient should be as low as possible, but compatible with the image quality necessary to obtain an adequate diagnosis or to guide treatment. Quality control of equipment is a prerequisite for achieving optimisation in diagnostic radiology. This was especially recognised for mammography as employed for breast cancer screening. Existing legislation in the Netherlands includes only a few criteria for equipment used in diagnostic radiology. In addition, the criteria are not all operational and measurement methods are lacking. Therefore, upon the initiative of the Dutch Ministry of Health, Welfare and Sports, the relevant professional societies, in collaboration with the former TNO Centre for Radiological Protection and Dosimetry, formulated eleven guidelines for quality control of equipment used in diagnostic radiology, including test procedures, test frequencies and limiting values. The implementation of quality control of equipment was included in the 1984 European Directive (84/466/Euratom) laying down basic measures for the radiation protection of persons undergoing medical examination or treatment. In the most recent European Directive on medical exposure (97/43/Euratom) the importance of quality control is stressed. In addition, the latter EC directive proposes the use of diagnostic reference levels for limiting the risks for patients undergoing diagnostic radiology. In the Netherlands preliminary reference levels for various procedures employed in diagnostic radiology are suggested. Finally, methods applied in the Netherlands for assessment of image quality are discussed.