To elucidate the presence of chronic hyperinsulinemia and its relation to clinical and biochemical parameters, 112 (53 females and 59 males) Chinese non-insulin-dependent diabetes mellitus (NIDDM) patients under chlorpropamide therapy were closely monitored for three years. Clinical and biochemical risk factors for chronic hyperinsulinemia were studied by regular monitoring of body weight, fasting insulin levels and various biochemical data. Chronic hyperinsulinemia was defined as a mean fasting level over 20 microU/mL (highest level observed in 35 non-diabetics). Among 112 diabetics, 52 cases (46.4%) showed chronic hyperinsulinemia. From simple linear regression analysis, female gender, high BMI and elevated triglyceride and uric acid levels were correlated with insulin levels (p < 0.05). The presence of diabetic complications (retinopathy, neuropathy and nephropathy) and the degree of glycemic control were not significantly different between the normoinsulinemic and hyperinsulinemic groups. In conclusion, 1) NIDDM patients treated with chlorpropamide showed higher fasting insulin levels with 46.4% of them meeting the criteria for chronic hyperinsulinemia; 2) female gender, uric acid, BMI and triglyceride were the risk factors correlated with chronic hyperinsulinemia; and 3) the presence of diabetic complications and diabetic control correlated poorly with chronic hyperinsulinemia.