In a study sample of 229 second-generation Japanese-American (Nisei) men, 79 with normal glucose tolerance, 72 with impaired glucose tolerance (IGT), and 78 with non-insulin-dependent diabetes, we have determined prevalence rates for certain conditions (ischemic heart disease, peripheral vascular disease, hypertension, retinopathy, neuropathy, and nephropathy) associated with diabetes. All subjects participated in a 75-g oral glucose tolerance test. World Health Organization (WHO) diagnostic criteria and information from the subject's medical history and personal physician were used to classify the subjects. Retinopathy was observed only in diabetic men in the study sample (11.5% of diabetic men). Furthermore, it was observed only in men who were receiving drug treatment for diabetes--40.0% of insulin-treated and 17.2% of sulfonylurea-treated men. Electrophysiologic evidence of peripheral neuropathy was observed in 46.2% of diabetic men and in 4.0% of nondiabetic (normal and IGT) men. For diabetic men with fasting serum glucose greater than or equal to 140 mg/dl, 63.8% had peripheral neuropathy and 19.1% had retinopathy, whereas for diabetic men with fasting serum glucose less than 140 mg/dl, 19.4% had neuropathy and none had retinopathy. For diabetic men with a diabetes duration of greater than or equal to 10 yr, 72.7% had neuropathy and 31.8% had retinopathy; with a diabetes duration of 5-9 yr, 70.6% had neuropathy and 11.8% had retinopathy; and with a diabetes duration of less than 5 yr, 20.5% had neuropathy and none had retinopathy. Nephropathy was distinctly uncommon, and among the measurements of kidney function, only proteinuria was clearly abnormal with diabetes. Prevalence rates of hypertension, peripheral vascular disease, and ischemic heart disease were highest in Nisei men with diabetes, lowest in men with normal glucose tolerance, and intermediate in men with IGT.(ABSTRACT TRUNCATED AT 250 WORDS)