N/ABackground: Mutations in mitochondrial DNA (mtDNA) are of potential importance in the patho- genesis of diabetes mellitus. MtDNA 3243 mutation (G->A) is famous and associated with insulin secretory defect, but it is found in only 0.52% of type 2 diabetes mellitus and it can explain only a small proportion of the patients with diabetes mellitus. Recently Poulton et al. showed that the 16189 variant (T C transition) in mtDNA was associated with insulin resistance in Caucasians. They showed that the prevalence of the 16189 variant in the American was 11% and the people with the 16189 variant had higher fasting insulin and HOMA insulin resistance than the people without the 16l89 variant. In this study, we investigated the prevalence of the 161S9 variant in Korean adults and its association with insulin resistance. Methods: We utilized the stored blood samples from community-based diabetes survey conducted in Yonchon County, Korea in 1993. We randomly selected 160 samples. We extracted the DNA from peripheral blood samples and examined the 16189 variant by PCR and restrictive enzyme digestion. We measured BMI, waist-hip ratio, blood pressure, fasting glucose, postprandial 2 hour glucose, fasting insulin, total cholesterol, triglyceride and HDL- cholesterol. HOMA insulin resistance and beta-cell function were calculated from fasting glucose and fasting insulin. Results: The prevalence of the 16189 variant in Korean adults was 28.8% (46/160), higher than in the American, but the same as in the Japanese. The subjects with the 16189 variant had higher fasting glucose and BMI than the subjects without the 16189 variant, but fasting insulin, HOMA insulin resistance, beta-cell function, cholesterol and blood pressure were not different between the two groups. Conclusion: The prevalence of the 16189 variant in the Korean is higher than in the Caucasian but the same as in the Japanese. Our results support that a frequent mitochondrial variant may contribute to the phenotype related to insulin resistance. However, further detailed studies must be made in a large number of patients.