Deaths among 35- to 44-year-old black and white men and women residing in Allegheny County, Pennsylvania, were investigated. All coroner-certified nontraumatic deaths and practitioner-certified deaths coded as heart, cerbrovascular, or arterial disease, diabetes mellitus, and sudden or ill-defined causes were studied. Using autopsy, coroner, hospital, physician, and/or informant information about medical history, characteristics, and circumstances of death, physicians validated the deaths as due to coronary heart disease (CHD) or another cause. In 1984 to 1989, 616 deaths were investigated, 384 of which were sudden (within 24 hours of onset). Overall CHD mortality was 35.4/100,000/y for white males, 8.4/100,000/y for white females, 61.3/100,000/y for black males, and 19.5/100,000/y for black females. Although rates varied widely, characteristics, circumstances, and disease history were similar across race-sex groups. CHD mortality was 73% higher in black than white males. Approximately 80% of CHD deaths were sudden.