A survey of accidents involving hazardous materials has been performed. A total of 5325 accidents taken from the database MHIDAS, covering from the beginning of this century up to July 1992, were used to study the contribution of different situations, activities, equipment, etc to the risks associated with hazardous materials. The data show the percentages of accidents involving transport (39%), process plants (24.5%) and storage (17.4%), as well as the frequency of occurrence of accidents in highly populated areas (66%), low-populated areas (12%) and rural areas (22%). The different types of accidents were also analysed, as well as their origin and causes. The consequences of the accidents, both with regard to people and economic losses, were assessed. The accumulated frequency-fatality curve has been plotted: the line follows approximately a straight line, with a slope of -0.84. Finally, several conclusions were derived about the effort which should be devoted to decreasing the risk in the future.