Irradiation accidents may unfortunately occur in all fields of activities, whether they are medical, industrial or scientific. They are usually classified in two categories, depending on the number of people involved: large-scale accidents on one hand and, on the other hand, events limited to small groups, mostly workers. The first are very rare, but well-documented. The latter occur more often, but no comprehensive report is yet available, especially for those with benign consequences. Whatever their seriousness, all these situations deserve careful analysis in order to draw appropriate conclusions and improve prevention. Although the number of radiation-related deaths is low (approximately 1 per year, during the last forty years, in Western countries), the frequency of such accidents remains constant, while the applications for the use of radiation increase. Analysis of accidents shows that most of the serious consequences might have been avoided or limited. This, once again, stresses the need of precise rules for every occupation involving ionizing radiation.