Trends in out-of-hospital coronary heart disease (CHD) death, a surrogate for sudden cardiac death (SCD), are important for understanding the decline in CHD mortality. Little is known about out-of-hospital CHD death without prior CHD diagnosis, the definition of unexpected SCD. The authors analyzed secular trends in CHD death and unexpected SCD over a 20-year period (1979-1998) to examine the association between prior CHD and SCD and to test the hypothesis that in-hospital deaths declined more than SCDs. The yearly decline in CHD mortality rates was 5.3% for in-hospital deaths and 1.8% for out-of-hospital deaths (p = 0.001). Among all SCDs, the proportion of unexpected SCD was 49%. Mortality rates for both unexpected SCD and SCD with prior CHD declined over time, but unexpected SCD declined at a slower rate than SCD with prior CHD (p = 0.001). The relative odds of prior CHD were higher among persons with SCD than among controls, but there was a modest decline in the magnitude of the association. Thus, during the past 20 years, the decline was greater for in-hospital CHD deaths than for SCDs. Since approximately half of the SCDs were unexpected and rates of these deaths declined less over time than rates of SCD with prior CHD, primary prevention is becoming increasingly more important in sustaining the decline in CHD mortality.