The value of mammography in symptomatic patients is now well established, but its use as a mass screening technique for asymptomatic women is still controversial.In the fourth chapter of this report, the National Committee on Radiation Protection and Measurements of the USA tries to provide a considered view on relative risks and benefits of mammography. An earlier chapter also contains some very useful descriptions of equipment and techniques and the measurements that should be performed to ensure that equipment is operating satisfactorily.