The relation of trans-fatty acid intake to fasting serum lipid concentrations was evaluated in a cross-sectional study of 748 men aged 43-85 y. Multiple-linear-regression analysis was used to adjust for age, body mass index, waist-to-hip circumference ratio, smoking status, physical activity, alcohol intake, total energy, dietary cholesterol and linoleic acid, and previous serum cholesterol concentration. Trans-fatty acid intake was directly related to total serum (r = 0.07, P = 0.04) and low-density-lipoprotein cholesterol (LDL) (r = 0.09, P = 0.01), and inversely related to high-density-lipoprotein (HDL) cholesterol (r = 0.08, P = 0.03). Trans-fatty acid intake was positively associated with the ratios of total to HDL cholesterol (r = 0.11, P = 0.002) and LDL to HDL cholesterol (r = 0.12, P = 0.001). The estimated ratios of total to HDL cholesterol were 4.4 and 4.9 for persons at the 10th (2.1 g/d) and 90th (4.9 g/d) percentiles of trans-fatty acid intake, respectively. On the basis of results from other studies, these ratios would correspond to a 27% increase in risk of myocardial infarction.