In most industrialized countries mortality data are the only medically relevant complete statistics for the description of health and disease in a population. Although mortality data reflect just the opposite of the state of health of a population, specific age and sex mortality rates are important indicators of the health status of a population and beyond that for the social system, e.g. for the effectiveness of the subsystem of health services. Validation studies show that the diagnoses on death certificates are much more reliable than generally thought. Scientists must have access to information from the original death certificates because otherwise the increasingly desirable studies on the threat of environmental noxae to the population cannot be carried out.