Trans-fatty acid intake is associated with coronary heart disease (CHD), but the atherogenic potential of individual trans-fatty acids (FA) from partially hydrogenated oils (18:1 and 18:2) or meat and dairy products (16:1 and 18:1) is unclear. Incident cases (n = 482) of a first nonfatal myocardial infarction (MI) were matched with population controls (n = 482) for age, gender and area of residence, all living in Costa Rica. Trans-FA in adipose tissue samples were assessed by gas chromatography. Odds ratios (OR) and 95% confidence intervals were calculated from conditional logistic regression models. Total adipose tissue trans-fat was positively associated with risk of MI. After adjusting for established risk factors and other confounders, the OR by quintiles of total trans-fat were 1.00, 1.34, 2.05, 2.22 and 2.94 (P-test for trend < 0.01). This association was attributed mainly to 18:2 trans-FA that were abundant in both adipose tissue and in partially hydrogenated soybean oil, margarines and baked products used by this population; OR = 1.00, 0.96, 2.09, 3.51 and 5.05 (P-test for trend < 0.001). Adipose tissue 16:1 trans-FA were also associated with MI; OR = 1.00, 1.57, 1.39, 1.34 and 2.58 (P-test for trend < 0.05). An association with 18:1 trans-FA was not detected. High 18:2 trans-FA in adipose tissue are associated with increased risk of MI. Because the use of hydrogenated oils is increasing worldwide, consumers should be aware of the harmful effects of products containing partially hydrogenated oils.