In the Münster Heart Study (PROCAM), 16,288 men aged 40.6 +/- 11.3 years (mean +/- S.D.) and 7328 women aged 36.0 +/- 12.3 years were enrolled between 1979 and 1991. Mean body mass indices (BMIs) were 25.6 +/- 3.3 and 23.8 +/- 4.1 kg/m2 in men and women, respectively. There was a graded and continuous positive interaction in both men and women between BMI, age and serum total cholesterol, low density lipoprotein (LDL) cholesterol, and blood pressure (both systolic and diastolic). High density lipoprotein (HDL) cholesterol tended to increase with age, but decreased in graded fashion with increases in BMI in both sexes. Triglyceride increased with BMI in both sexes and with age in women, but decreased in the older age groups of overweight and obese men. Though fasting blood glucose increased with age and BMI in both sexes, the increase was more marked in women. Among the 10,856 men aged 36-65 years at study entry, 313 deaths occurred within a follow-up period of 7.1 +/- 2.4 years. Among these men, increased mortality was seen at high BMIs in both smokers and non-smokers and was caused by coronary heart disease (CHD). Increased mortality at low BMI was seen in smokers but not in non-smokers and was due to an increase in cancer deaths. The BMI-associated increase in CHD death was completely accounted for by the factors contained in the Münster Heart Study (PROCAM) risk algorithm, indicating that the effect of overweight and obesity on CHD is mediated via other risk factors.