An association between childhood cognitive ability measured with IQ-tests and coronary heart disease (CHD) incidence has been reported recently. It is not clear from those studies to what extent the increased relative risk associated with lower cognitive ability may be explained by CHD risk factors. This study aims to investigate the association between cognitive ability measured at age 18-20 and incidence of CHD, acute myocardial infarction (AMI), and stroke among middle aged men adjusting for risk factors for CHD over the life course. Data on cognitive ability, and other risk factors for CHD (height, parental cardiovascular diseases (CVD) mortality, blood pressure, smoking, risky use of alcohol, BMI), were collected from 49,321 men, born in 1949-51, at conscription for compulsory military training in 1969/70 in Sweden. Information on socioeconomic factors in childhood (socioeconomic position and crowded housing) and adulthood (education, socioeconomic position, and income), as well as information on mortality and morbidity, was collected through national registers. Cognitive ability showed an inverse and graded association with CHD incidence. Adjustment for indicators of poor childhood circumstances, behavioural factors measured in late adolescence, and adult social circumstances strongly attenuated the increased risks of CHD and AMI. The contribution from adult social circumstances, after adjustment from all other factors, was very small. After adjustment for all risk factors no significantly increased relative risk was seen for stroke incidence. After adjustment for risk factors over the life course, the risk of CHD and AMI associated with cognitive ability decreased substantially, and was of borderline significance. Given the results from this study it is unlikely that cognitive ability is a risk factor on its own for CHD, AMI and stroke among men below 54 years of age.