The social impact of public projects could be very important; the bigger the project, the bigger the impact it is possible to expect. Therefore, it is not enough to define a precise objective of the project which has to be achieved, even if this is the most important element of the project management. It is necessary to take care of needed resources, and the efficiency of their utilization, in order to reach defined objectives. There are many methods for the assessment of efficiency, so it is not so big a problem to assess, if the project is efficient enough. However, each project (and especially big projects or megaprojects) is connected with a specific number of factors, which can threaten the achievement of project objectives and cause the project uncertainty. The paper deals with the risk management and risk assessment of big projects and megaprojects in the Czech Republic.