In order to prepare Belgian participation in the International Study "Monitoring of trends and determinants in cardiovascular disease (MONICA)", a pilot project for registration of acute myocardial infarctions was organized in the Flemish city of Ghent and the Walloon city of Charleroi. Thanks to the collaboration of 449 general practitioners and 17 hospitals, 790 acute coronary events (fatal and non-fatal) were registrated during one year among the 251 000, 25 to 69 year old, inhabitants of Ghent and Charleroi. The registration procedures, strictly standardized between the two cities, allowed comparison of the incidence data. In males, the total incidence of acute myocardial infarction is 10% higher in Charleroi than in Ghent. In the female population, the incidence is 37% higher in the Walloon city compared to the Flemish city.