AbstractThis paper reports a comparative analysis of citizen evacuation response to three different types of environmental threats: a riverine flood, a volcanic eruption, and the nuclear reaction accident at Three Mile Island, Pennsylvania. While there have been numerous discussions in the theoretical literature regarding the extent to which human response to nuclear and nonnuclear threats are likely to be comparable, to date there have been no empirical studies of the phenomenon. It was found that citizen belief in real situational danger and warnings from authorities were most frequently cited by evacuees as reasons for leaving inbothnuclear and nonnuclear incidents. Mass media warnings were infrequently cited as important reasons for evacuating, and social network contacts were relatively more important to evacuation decision making in the natural disasters than at Three Mile Island. For both the natural disasters and the nuclear accident, most citizens who did not evacuate chose not to do so because they did not believe that a real danger existed.