Myocardial infarction incidence rate declined 3-5% per year during 1982-1992 in the Danish study population of the WHO MONICA Project. We examined whether smoking habits, alcohol intake, dietary habits and physical activity levels changed in the population during the same period. Data from 6695 men and women of ages 30, 40, 50 and 60 y, examined in 1982-4, in 1986-7, and in 1991-2, were analysed to estimate trends. A summary healthy eating index and six scores derived by factor analysis were used to analyse food frequency data. The percentage of smokers declined 1.6% per year in men, and 1.0% per year in 30-, 40- and 50-y-old women, but increased 0.9% per year in 60-y-old women. The percentages of heavy cigarette smoking men and women nevertheless remained constant and close to 30%. Total alcohol intake declined among 30-y-olds, but appeared constant in other age groups. However, among 60-y-old men and among women over 30, the percentage of wine-drinkers rose from 6-11% in 1982-4 to 9-18% in 1991-2. Only 60-y-old men became more physically active at work and only 30-y-old women more so in leisure times. The percentage of individuals with a low healthy eating index decreased and the percentage with a high index increased. More importantly, dietary factor scores showed trends suggesting that very profound and potentially beneficial changes in dietary habits occurred. Lifestyle in the DAN-MONICA population changed in several ways that may have contributed to the declining incidence of myocardial infarction during the 1980s.