The objective of this study was to examine whether it is through their low control beliefs that low socio-economic status groups have higher risks of heart disease, and to examine whether this mechanism is more substantial than and independent of the mechanism via classical coronary risk factors. In a population-based prospective cohort study, participants were selected from 27 general practices in the north-eastern part of The Netherlands. In 1993, there were 3888 men and women, 57 years and older, who were without prevalent heart disease. During the 5-year follow-up period, 287 cases of incident heart disease (acute myocardial infarction and/or congestive heart failure) were registered (7%). Persons with a low socio-economic status had higher risks of heart disease (RR = 1.45 (95% CI: 1.06 - 1.99)) compared with their high status counterparts. On average, 4 percent of the socio-economic differences were accounted for by the classical coronary risk factors (e.g. smoking, hypertension) compared with 30 percent by the control beliefs. The contribution of the latter was largely independent of the former. Our findings support the hypothesis that socio-economic inequalities in heart disease-at least in middle-aged and older persons-may be based upon differences in control beliefs, more than upon differences in smoking rates and other classical risk factors.