Clinicopathologic and epidemiological aspects of coronary artery disease (CAD) in relation to sudden death (SD) were studied in three postmortem series, two of sudden cardiac death and one of male violent death. There appears to be a critical level of severity of CAD which determines the risk of SD. The more severe the CAD within this range, the higher is the risk. Every annual cohort of SDs includes many patients with extremely severe, or 'burned-out', disease. CAD alone, however, is not a selective factor for sudden or not-sudden death. Epidemiological analysis (a) determines the age and frequency of persons reaching the critical risk level of CAD severity in the population (atherogenic factors); (b) influences the selection of the SD victims from the critical population (precipitating factors), and (c) determines the individual variation of CAD severity with which coronary heart disease and SD manifest themselves (sensitising and protecting factors).