[en] Unforeseen radiation exposures may be caused by technical or human faults in the utilization of radioactive devices, namely radionuclide sources, as well as from the peaceful uses of nuclear energy; the first instance is in general the more common one. The paper discusses the principal basis for health intervention planning in the case of possible accidental exposures of workers and/or the population to ionizing radiation, also with reference to hypothetical accidents at nuclear power stations. For this last purpose an important aspect is the definition of the 'source term' problem. The main differences existing between 'conventional' and radiation emergencies in the pre-planning of technical and health safety operations are discussed. Even if the general organizational planning is based on similar operating structures, radiation emergencies require a somewhat different approach. Besides the specialized aspects of prophylaxis and therapy which are needed in these cases, radiation emergencies call for a comparison of the social cost, the possible health detriment induced by health-related countermeasures and the specific radiation risk in a single case. In many instances, furthermore, a key role may also be played by psychological factors. Following this philosophy, a flexible organization plan has been drawn up, which consists of three-steps as follows: (1) local and/or regional level; (2) national level; (3) European or international level. For the first two levels, besides the possibility of utilizing health services, there is provision to arrange them into structures of increasing complexity, using modular, integrated and fixed operative units to adapt the intervention to specific aspects of each accident or emergency. The third level is represented by the WHO International Centre of Radiopathology (ICR) in Paris. An official agreement was recently signed by the ENEA and the Centre. (author)