To investigate the association of a westernized lifestyle and coronary risk factors in the Japanese population, we studied Japanese-Americans originally from Hiroshima who were living in Hawaii and Los Angeles (JA group, N = 986) as well as Japanese currently residing in Hiroshima (JH group, N = 852) between 1982 and 1996. All subjects underwent a dietary survey, physical examination, 75 g oGTT, serum lipid and lipoprotein measurements and ECG recording. The JA group had a higher consumption of animal fat and simple carbohydrates, but a lower intake of complex carbohydrates than the JH group, although the total calorie intake was similar between the two groups. Strenuous physical activity was less common in the JA group. Both the mean body mass index (BMI) and the waist/hip (W/H) ratio were significantly higher in JA men that JH men. The mean W/H ratio was also significantly higher in JA women than JH women despite the similarity of BMI. The age- and, BMI adjusted mean values of serum cholesterol (TC), triglyceride (TG), and LDL-C, but not HDL-C were significantly higher in the JA group compared to the JH group. LDL subclass pattern B was more prevalent in the JA group. The age-, sex-, and BMI adjusted prevalence of diabetes and hypertension (WHO criteria) were also significantly higher in the JA group. Furthermore fasting (F)-IRI and the IRI response to a glucose load were significantly higher in the JA group. F-IRI was correlated positively with TG and negatively with HDL-C and LDL particle size in the JA group suggesting the importance of insulin resistance in the abnormal lipid metabolism of the JA subjects. The age-adjusted prevalence of abnormal Q wave in resting ECG was significantly higher in the JA group. Furthermore, the crude death rate due to cancer and cerebrovascular disease has not changed over the years in the JA group, whereas the death rate from ischemic heart disease has markedly increased and in recent years, has almost reached the level in Caucasians. These results suggest that a westernized lifestyle amplifies many risk factors for atherosclerosis and has a strong impact on the development of ischemic heart disease in the Japanese.