In Seattle, Washington, the prevalence of diabetes was 20% in second-generation (Nisei) Japanese-American men and 16% in Nisei women 45-74 years old, while the prevalence of impaired glucose tolerance (IGT) was 36% in Nisei men and 40% in Nisei women. Hyperglycemia was less and duration of diabetes shorter in women. Related to diabetes and IGT in Nisei were higher fasting plasma insulin levels and central (visceral) adiposity. Prevalence of diabetes was low among the younger (34-53 years old) third-generation (Sansei) men and women. Among self-reported non-diabetic Sansei, however, prevalence of IGT was 19% in men and 29% in women, and IGT was associated with both increased fasting plasma insulin levels and more visceral fat, suggesting that many Sansei are at risk of future diabetes. An important lifestyle factor in the development of NIDD in Japanese Americans appeared to be dietary saturated (animal) fat. Another factor may be physical inactivity. In Japanese-American women, menopause also appeared to be an important risk factor. These risk factors may be related to fostering the accumulation of visceral fat and the development of insulin resistance. Five-year follow-up examinations performed in non-diabetic Nisei men and women have yielded additional information concerning the prognosis of IGT. Of those women who were IGT at baseline, 34% were diabetic at follow-up while 17% returned to normal. In men who had been IGT at baseline, 18% were diabetic at follow-up while 36% returned to normal. Over the 5-yr follow-up interval, proportionally more women progressed from normal to IGT (54%) then went from IGT to normal (17%). For men, roughly equal proportions went from normal to IGT (37%) as from IGT to normal (36%). It would therefore appear that greater proportions of Nisei women are progressing to IGT and to NIDD than are Nisei men. This observation may be related to the increased risk of developing central obesity and insulin resistance following menopause. Prevalence of cardiovascular disease (hypertension, peripheral vascular disease, and/or coronary heart disease) was increased in Japanese Americans with IGT and NIDD. Neuropathy and retinopathy were associated only with NIDD.