Introduction: Inorganic arsenic (iAs) has been associated with type 2 diabetes in adults, but there are few studies in children. We assessed the associations of peripubertal urinary iAs concentrations with insulin resistance (IR) at adolescence among boys in Chapaevsk, Russia.Methods: 516 8-9 year-old boys were enrolled from 2003-2005 in a prospective cohort study of environmental exposures, growth and puberty. At study entry, parents/guardians completed medical history and demographic questionnaires, and speciated urine As concentrations (µg/L) were measured with ion chromatography coupled to ICP-MS; LOD=0.5, except arsenate (AsV) =1.0. Follow-up included annual physical exams and biennial collection of fasting blood samples. At ages 10-13 years, 430 boys had IR calculated by the homeostatic model. ΣiAs was calculated as the sum of arsenite (AsIII) + AsV, and levels were categorized as low (<1.0), medium (1.0-2.0), or high (>2.0). AsIII and AsV were also dichotomized as high vs. low (≥ vs. < LOD). Total As (tAs), calculated as ΣiAs + monomethylarsonic acid + dimethylarsenic acid, was categorized by quartiles. Associations of As species with IR were examined by multivariable generalized estimating equations for repeated measures, adjusted for urine specific gravity, age, and BMI.Results: 9.1% of boys had IR. The medians (max) of tAs, AsIII, AsV, and ΣiAs were 5.9 (254), 0.4 (57), 0.2 (15.7) and 0.7 (62) µg/L, respectively. In multivariable models, compared to low ΣiAs, the OR (95% CI) associated with medium and high ΣiAs were 1.90 (0.85, 4.28) and 2.42 (0.90, 6.52), p-trend=0.06. Of the iAs species, only AsV was associated with significantly increased odds of IR, with OR=2.75 (95% CI: 1.17, 6.47). tAs was not associated with IR.Conclusion: In this Russian cohort, higher peripubertal iAs was associated with increased odds of IR over four years of follow-up.Funded by EPA R82943701, NIEHS ES014370, ES000002 & ES024907.