Although 36% of US men are normal weight (BMI <25 kg/m(2)), the health benefits of greater leanness in normal-weight individuals are seldom acknowledged. To assess the optimal body weight with respect to minimizing coronary heart disease (CHD) risk, we applied Cox proportional hazard analyses of 20,525 nonsmoking, nondiabetic, normal-weight men followed prospectively for 7.7 years, including 20,301 who provided follow-up questionnaires. Two-hundred and forty two men reported coronary artery bypass graph (CABG) or percutaneous transluminal coronary angioplasty (PTCA) and 82 reported physician-diagnosed incident myocardial infarction (267 total). The National Death Index identified 40 additional ischemic heart disease deaths. In these normal-weight men, each kg/m(2) decrement in baseline BMI was associated with 11.2% lower risk for total CHD (P = 0.005), 13.2% lower risk for nonfatal CHD (P = 0.002), 19.0% lower risk for nonfatal myocardial infarction (P = 0.01), and 12.2% lower risk for PTCA or CABG (P = 0.007). Compared to men with BMI between 22.5 and 25 kg/m(2), those <22.5 kg/m(2) had 24.1% lower total CHD risk (P = 0.01), 27.9% lower nonfatal CHD risk (P = 0.01), 37.8% lower nonfatal myocardial infarction risk (P = 0.05), and 27.8% lower PTCA or CABG risk (P = 0.02). In nonabdominally obese men (waist circumference <102 cm), CHD risk declined linearly with declining waist circumference. CHD risk was unrelated to change in waist circumference between 18 years old and baseline except as it contributed to baseline circumference. These results suggest that the optimal BMI for minimizing CHD risk lies somewhere <22.5 kg/m(2), as suggested from our previous analyses of incident diabetes, hypertension, and hypercholesterolemia in these men.