Consistent reductions in cardiovascular mortality have been demonstrated in recent years in most developed countries. From official mortality data for the period 1969-1987, we have recently detected a similar trend in Italy. The decline started in the second half of the 1970s and was more pronounced in the northern part of the country. To identify the determinants of these trends, the World Health Organization Monitoring Cardiovascular Diseases (WHO MONICA) Project was set up. There are 39 participating centers spread over 26 countries worldwide. In the Brianza area, one of the three Italian areas that joined the project from the beginning, two population surveys and 5 years of mortality records have been completed. Provisional results and methodological issues of quality control and data collection are discussed in this paper, together with the implications for prevention and treatment.