Microalbuminuria in non-diabetic subjects is reportedly associated with increased cardiovascular morbidity and mortality. The prevalence of microalbuminuria in non-diabetic subjects varies widely from 5-6% in the UK and USA to 30-55% in Finland, Mexico, or Australian Aborigines. We studied cross-sectionally 497 clinically healthy, non-diabetic subjects more than 40 years of age who were living in Seoul, Korea for the prevalence of microalbuminuria and various cardiovascular risk factors. Urinary albumin-to-creatinine ratio (UACR) was determined in morning spot urine samples. Subjects were divided into normoalbuminuria (UACR < 2 mg/mmol) and microalbuminuria (UACR > or = 2 mg/mmol) groups. A total of 61 (12.2%) out of 497 subjects were found to have microalbuminuria. Subjects with microalbuminuria had significantly higher values in age, body mass index (BMI), waist-to-hip ratio in women, systolic and diastolic blood pressure, prevalence of hypertension, plasma cholesterol and triglyceride, and fasting plasma insulin. When subjects with microalbuminuria were compared with age-, sex-, and BMI-matched controls without microalbuminuria, systolic and diastolic blood pressure, and fasting plasma insulin concentrations were higher in microalbuminuric subjects. Multiple logistic regression analysis showed that fasting plasma insulin level and systolic blood pressure were independently associated with microalbuminuria. These results indicate that the prevalence of microalbuminuria in Korean non-diabetic subjects is lower than that in Mexico and Finland, but similar to that in Caucasians from the UK and USA, or in Pima Indians. Also, microalbuminuria in Korean non-diabetic subjects is associated with atherosclerotic risk factors such as hyperinsulinemia and hypertension, suggesting that microalbuminuria in these subjects may be a feature of insulin resistance syndrome.