This study examines the joint and separate influence of birth weight and body mass in young adulthood on subsequent coronary heart disease (CHD) risk. A cohort of 9,143 men born in Copenhagen, Denmark, in 1953, for whom information on birth weight and body weight and height around age 19 years were retrieved from birth certificates and conscript records, respectively, were followed from 1978 until 2005 (between age 25 and 52 years) for incident fatal and non-fatal CHD. Data on CHD were obtained through record linkage to the Cause of Death Registry and the National Patient Registry. During follow-up, a total of 475 men had a CHD diagnosis. Men with low birth weight, high body mass index (BMI) at age 19, a father from the working class, and low educational level at age 19 had an increased risk for CHD. Birth weight was inversely associated with CHD only in men with BMI of 25 kg/m(2) or above. Adjustment for childhood social circumstances and educational status at age 19 had minor influence on the estimates. In conclusion, BMI in young adulthood seems to be strongly associated with the risk of CHD before age 52, and birth weight seem to modify the association. The risk estimates is highest for individuals with a combination of low birth weight and overweight in young adulthood.