Oxidative stress has been linked to many diseases, but little information exists on biomarkers of oxidative stress in healthy children. The purpose of this study was to describe factors that correlate with urinary F2-isoprostanes, an indicator of oxidative stress, and to establish normal concentrations of F2-isoprostanes in children at risk to develop type 1 diabetes mellitus. Creatinine-adjusted urinary F2-isoprostanes were assessed in 342 Denver children under the age of 7 years, from whom we had collected data during 769 clinic visits from August 1997 through January 2001 (mean 2.3 visits per child). Children were identified by newborn screening for HLA-markers, of varying degrees of prediction, for the development of type 1 diabetes. Plasma antioxidants and carotenoids, age at clinic visit, vitamin supplement use, exposure to environmental tobacco smoke, gender, and race were evaluated as correlates to the degree of oxidative stress, using mixed models for longitudinal data. F2-isoprostane levels were highest in infancy and decreased nonlinearly until 7 years. Female gender, HLA-DR3/4 genotype, higher plasma gamma-tocopherol:total lipids ratio, and lower alpha-carotene:total lipids ratio correlated with higher F2-isoprostane levels. Normal values in this healthy population can be used as the basis for future studies of disease mechanisms involving oxidative stress.