OBJECTIVE - To investigate whether the peripheral blood mtDNA (pb-mtDNA) content is decreased and linked to insulin resistance in the offspring of type 2 diabetic patients. RESEARCH DESIGN AND METHODS - A total of 82 offspring of type 2 diabetic patients and 52 age-, sex-, and BMI-matched normal subjects from the Mokdong, Korea, population were selected for this study by stratified, randomized sampling. Of the offspring of diabetic patients, 52 had normal glucose tolerance (NGT), 21 had impaired glucose tolerance (IGT), and 9 had newly diagnosed type 2 diabetes. The pb-mtDNA content was measured by real-time polymerase chain reaction with a mitochondria-specific fluorescent probe, normalized by a nuclear DNA, 28S rRNA gene. The associations between pb-mtDNA content and several parameters of insulin resistance were studied. RESULTS - The pb-mtDNA contents tended to be lower in the 82 offspring of type 2 diabetic patients (1,084.7 ± 62.6 vs. 1,304.0 ± 99.2 in the offspring and control subjects, respectively, P = 0.051) and was significantly lower in the combined NGT and IGT offspring group (NGT + IGT, 1,068.0 ± 67.8, P < 0.05) than in the control subjects. In NGT+IGT offspring, the pb-mtDNA content was significantly correlated with logarithmically transformed insulin sensitivity (r = 0.253, P < 0.05) and was the main predictor of insulin sensitivity. CONCLUSIONS - Quantitative mtDNA status might be a hereditary factor associated with type 2 diabetes and could serve as an indicator for insulin sensitivity.