Nuclear disasters are rare but due to their catastrophic consequences require a high level of preparedness based on careful analysis of past experience. In 2011 while the nuclear disaster of Chernobyl could be reviewed based on 25 years of experience, a new disaster of similar dimensions occurred at the Fukushima nuclear power plant in Japan. Whereas the events leading to the reactor failure, the technical conditions and the course of the accident differed widely between the two disasters, their consequences in terms of acute and long-term radioactive contamination, and hence their public health implications were rather similar. The purpose of this session is to review the events during and following the two accidents, and from a public health point of view, to analyze the experience in terms of decisions on immediate action, individual and collective exposure monitoring, dispatching of immediate and long-term clean-up personnel, and evacuation measures. The epidemiological evidence on health consequences of the Chernobyl nuclear disaster will be reviewed both for the clean-up workers (liquidators) and for the population living at different distances from the exploded reactor. Some striking discrepancies between disease estimates from official and advocacy sources will be analyzed, and the need for further monitoring and epidemiological research will be discussed in the light of recent health complaints among children living in moderately contaminated areas around Chernobyl and children of the second generation whose parents had been moved from the evacuation zone when they were children themselves. Finally, the scope of human suffering related to these nuclear accidents will be looked at from the perspective of long-term prevention by replacing nuclear power by the decentralized production of renewable energy.