This paper is a shortened version of an NRPB document that reviewed the deterministic effects on human health likely to arise from serious overexposure to ionising radiation. Little new primary information on deterministic effects has become available in recent years. However, advances in techniques for data analysis have been made, particularly in describing the sigmoid dose-effect relationships, effects of dose rate and radiation quality. These are presented in a form suitable for use in modelling the consequences to populations of serious radiological incidents.