Investigators in eight communities collected aortas, right coronary arteries, blood, and associated information from 390 males, 15 to 34 years of age, who died of violent causes. Pathologists at central laboratories graded the arteries for atherosclerotic lesions, and serum lipoprotein cholesterol and thiocyanate concentrations were measured. The percentage of intimal surface involved with atherosclerotic lesions in both the aorta and the right coronary artery was positively associated with serum very low—density lipoprotein + low-density lipoprotein cholesterol concentration and negatively associated with serum highdensity lipoprotein cholesterol concentration. The serum thiocyanate concentration, a marker for smoking, was strongly associated with prevalence of raised lesions, particularly in the abdominal aorta. The effect of smoking was not explained by lipoprotein levels. Blacks had more extensive total surface involvement of the aorta after adjustment for lipoprotein cholesterol levels and smoking. These associations indicate that serum lipoprotein cholesterol concentrations and smoking are important determinants of the early stages of atherosclerosis in adolescents and young adults.