ABSTRACT: Most accidents and other related events are often associated with uncertainties. It is therefore essential to develop risk analysis systems and to avoid its occurrence. The occurrence of accidents and incidents in underground structures is not as unusual as in other geotechnical structures. However the dissemination of these events are not common due to the legal problems involved. There is a general the tendency to minimize the dissemination of the involved damages and their causes exist. As a consequence, the number of reports concerning accidents in tunnels and other underground structures is relatively reduced. A review of general safety aspects in underground structures is analyzed in this lecture, namely different types of accidents and their consequences. The main causes of accidents and other deteriorations are described and typified, such as no adequate geotechnical studies, errors in the planning stage and in the calculations namely by numerical codes, errors during the construction or rehabilitation phase, and during the exploitation of the underground structures. Accidents and incidents in underground hydroelectric projects, in transportation tunnels and in urban subway systems are referred. The interaction of urban tunnels on the existing surface and subsurface infrastructures and the damage associated is also mentioned.