The WHO MONICA Project is a 10-year study that monitors deaths due to coronary heart disease (CHD), acute myocardial infarction, coronary care, and risk factors in men and women aged 35 to 64 years in defined communities. This analysis of methods and results of coronary event registration in 1985 through 1987 provides data on the relation between CHD morbidity and mortality. Fatal and nonfatal coronary events were monitored through population-based registers. Hospital cases were found by pursuing admissions ("hot pursuit") or by retrospective analysis of discharges ("cold pursuit"). Availability of diagnostic data on identified nonfatal myocardial infarction was good. Information on fatal events (deaths occurring within 28 days) was limited and constrained in some populations by problems with access to sources such as death certificates. Age-standardized annual event rates for the main diagnostic group in men aged 35 to 64 covered a 12-fold range from 915 per 100,000 for North Karelia, Finland, to 76 per 100,000 for Beijing, China. For women, rates covered an 8.5-fold range from 256 per 100,000 for Glasgow, UK, to 30 per 100,000 for Catalonia, Spain. Twenty-eight-day case-fatality rates ranged from 37% to 81% for men (average, 48% to 49%), and from 31% to 91% for women (average, 54%). There was no significant correlation across populations for men between coronary event and case-fatality rates (r = -.04), the percentages of coronary deaths known to have occurred within 1 hour of onset (r = .08), or the percentages of known first events (r = -.23). Event and case-fatality rates for women correlated strongly with those for men in the same populations (r = .85, r = .80). Case-fatality rates for women were not consistently higher than those for men. For women, there was a significant inverse correlation between event and case-fatality rates (r = -.33, P < .05), suggesting that nonfatal events were being missed where event rates were low. Rankings based on MONICA categories of fatal events placed some middle- and low-mortality populations, such as the French, systematically higher than they would be based on official CHD mortality rates. However, rates for nonfatal myocardial infarction correlated quite well with the official mortality rates for CHD for the same populations. For men (age 35 to 64 years), approximately 1.5 (at low event rates) to 1 (at high event rates) episode of hospitalized, nonfatal, definite myocardial infarction was registered for every death due to CHD. The problem in categorizing deaths due to CHD was the large proportion of deaths with no relevant clinical or autopsy information. Unclassifiable deaths averaged 22% across the 38 populations but represented half of all registered deaths in 2 populations and a third or more of all deaths in 15 populations. The WHO MONICA Project, although designed to study longitudinal trends within populations, provides the opportunity for relating rates of validated CHD deaths to nonfatal myocardial infarction across populations. There are major differences between populations in nonfatal as well as fatal coronary event rates. They refute suggestions that high CHD mortality rates are associated with high case-fatality rates or a relative excess of sudden deaths. The high proportion of CHD deaths for which no diagnostic information is available is a cause for concern.