The Copenhagen City Heart Study was designed to evaluate the incidence of and risk factors for cardiovascular disease. Information about potential risk factors was collected from 14,223 persons during an initial examination (1976-78) (attendance rate 74%). Information about new cases of acute myocardial infarction (AMI) was obtained from a second examination (1981-83), hospital registries and death registries up to December 31st 1983. This article deals with 'basic' risk factors, namely age, sex, some factors presumably of genetic character (family history of AMI, early parental death, height and earlobe crease) and social factors such as length of school education, income and marital status. The Cox regression model was used. As expected, the risk of first AMI increased with age and was highest among males. Earlobe crease and family history of AMI were found to be significant risk factors, the relative risk being 1.4 for both. No effect was found of early parental death and height. Low grade of education was associated with a higher risk, significantly so only in women, the relative risk being 1.7. Low income carried an increased risk, particularly for females. Cohabitation carried a higher risk, most pronounced in the low income group. Approximately half the effect of education was exerted through its influence on income and marital status.