Background Socioeconomic differentials have been described in the risk of coronary heart disease (CHD) but the extent to which these differentials are explained by lifestyle factors has been examined to a lesser degree. We have examined the contribution of socio-economic factors to risk of CHD in a large cohort study in France and Northern Ireland. Methods In all, 10 593 men aged 50-59 years were examined between 1991 and 1994 in centres in Northern Ireland, Lille, Strasbourg, and Toulouse, Details were obtained for a number of socio-economic indicators from the men at the baseline examination. Men were also screened for evidence of CHD and followed annually by questionnaire for incident cases of coronary disease. Coronary events (coronary deaths, myocardial infarction, and angina) were documented by clinical records and were reviewed by an independent medical committee. Results In all, 842 men (8%) showed some evidence of CHD at screening examination and these men were more likely to be living in poorer material circumstances, be unemployed, or have had less full-time education than men without CHD at screening in both France and Northern Ireland. These relationships persisted following adjustment for all known risk factors for CHD. Among men who were initially free of CHD there were clear socio-economic differentials (years of fulltime education, unemployment, and educational level) in the distribution of several risk factors for CHD, notably smoking habit (which differs in France and Northern Ireland), systolic blood pressure, body mass index, and fibrinogen. Total cholesterol in contrast showed no socio-economic differential whilst those with a shorter period of full-time education and the unemployed tended to be high consumers of alcohol. In this cohort of then free of CHD at baseline few socioeconomic indicators showed relationships with risk of CHD by 5 years of follow-up. Only years in full education, educational level, and unemployment status when adjusted only for age and country showed significant relationships with CHD risk, but these became non-significant following adjustment for major CHD risk factors. Conclusions Socio-economic differentials in long-term risk of CHD are apparent in both cohorts of men from France and Northern Ireland, particularly in men with evidence of CHD at baseline. Among men free of CHD at baseline, although there is strong evidence of socio-economic differentials in cardiovascular risk factors these do not contribute independently to risk of CHD at 5 years of follow-up in this large cohort of men from France and Northern Ireland.