The authors examined the associations of dietary fat and specific types of fat with risk of coronary heart disease (CHD) among 78,778 US women initially free of cardiovascular disease and diabetes in 1980. They documented 1,766 incident CHD cases (including 1,241 nonfatal myocardial infarctions and 525 CHD deaths) during 20 years of follow-up. Polyunsaturated fat intake was inversely associated with CHD risk (multivariate relative risk (RR) for the highest vs. the lowest quintile = 0.75, 95% confidence interval (CI): 0.60, 0.92; p(trend) = 0.004), whereas trans-fat intake was associated with an elevated risk of CHD (RR = 1.33, 95% CI: 1.07, 1.66; p(trend) = 0.01). The associations between intakes of polyunsaturated fat and trans-fat with CHD risk were most evident among women younger than age 65 years (for polyunsaturated fat, RR = 0.66, 95% CI: 0.50, 0.85; p(trend) = 0.002 and for trans-fat, RR = 1.50, 95% CI: 1.13, 2.00; p(trend) = 0.01). The inverse association between polyunsaturated fat intake and CHD risk was strongest among women whose body mass index was >or=25 kg/m(2). Findings continue to support an inverse relation between polyunsaturated fat intake and CHD risk, particularly among younger or overweight women. In addition, trans-fat intake was associated with increased risk of CHD, particularly for younger women.