This paper presents the history of the discovery of ionizing radiation, as well as its biological effects and the resulting need to control subsequent health risks. It describes the historic evolution of risk control in radiodiagnosis in Brazil, demonstrating that it may be associated not only to the dose received, but also to errors in diagnosis and to costs to the health system. It is stressed that sanitary regulations have a broad remit of social co-responsibility to involve all the players with a view to safeguarding health.