Background: Several epidemiologic studies suggest a slightly increased risk of type 2 diabetes in relation to background levels of dioxins. Little is known about how serum dioxins might affect insulin resistance, a hallmark of type 2 diabetes. We examined the association between exposure to dioxins and insulin resistance. Methods: We investigated 1234 nondiabetic persons living near a deserted pentachlorophenol factory. Using high-resolution gas chromatography/high-resolution mass spectrometry and blood biochemistry tests, we measured serum dioxins, fasting glucose, and insulin. Finally, we examined associations between serum dioxin levels and the homoeostasis model assessments of insulin resistance and pancreatic β-cell function. Results: Participants with insulin resistance (index at or above the 75th percentile) had higher dioxin levels (24.3 vs. 19.8 pg WHO98-TEQDF/g lipid) than those without insulin resistance. In both the crude and adjusted models, insulin resistance increased with serum polychlorinated ibenzo-p-dioxins and dibenzofuran (PCDD/F) levels. We found a slight monotonic increase in insulin resistance across the serum PCDD/F categories (P for the trend <0.001). Groups with serum dioxin levels higher than 20.5 pg WHO98-TEQ DF/g lipid had higher insulin resistance (adjusted odds ratios of 2.7, 3.5, and 5.0 for 50th to <75th, 75th to <90th, and ≥90th percentile, respectively) compared with the reference group (<9.6 pg WHO 98-TEQDF/g lipid [< 10th percentile]). Conclusions: After adjusting for confounding factors, we found a positive association between serum dioxins and the prevalence of insulin resistance.