The physiological relevance C-3 epimer of 25-hydroxyvitamin D (3-epi-25(OH)D) is not well understood among youth. The objective of this study was to assess whether demographic/physiologic characteristics were associated with 3-epi-25(OH)D3 concentrations in youth. Associations between 3-epi-25(OH)D3 and demographics and between 3-epi-25(OH)D3, total 25-hydroxyvitamin (25(OH)D) (25(OH)D2 + 25(OH)D3), total cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides were examined in racially/ethnically diverse schoolchildren (n = 682; age, 8-15 years) at Boston-area urban schools. Approximately 50% of participants had detectable 3-epi-25(OH)D3 (range 0.95-3.95 ng/mL). The percentage of 3-epi-25(OH)D3 of total 25(OH)D ranged from 2.5% to 17.0% (median 5.5%). Males were 38% more likely than females to have detectable 3-epi-25(OH)D3 concentrations. Both Asian and black race/ethnicity were associated with lower odds of having detectable 3-epi-25(OH)D3 compared with non-Hispanic white children (Asian vs. white, odds ratio (OR) 0.28, 95% confidence interval (CI) 0.14-0.53; black vs. white, OR 0.38, 95%CI 0.23-0.63, p < 0.001). Having an adequate (20-29 ng/mL) or optimal (>30 ng/mL) 25(OH)D concentration was associated with higher odds of having detectable 3-epi-25(OH)D3 than having an inadequate (<20 ng/mL) concentration (OR 4.78, 95%CI 3.23-6.94 or OR 14.10, 95%CI 7.10-28.0, respectively). There was no association between 3-epi-25(OH)D3 and blood lipids. However, when considering 3-epi-25(OH)D3 as a percentage of total 25(OH)D, total cholesterol was lower in children with percent 3-epi-25(OH)D3 above the median (mean difference -7.1 mg/dL, p = 0.01). In conclusion, among schoolchildren, sex, race/ethnicity, and total serum 25(OH)D concentration is differentially associated with 3-epi-25(OH)D. The physiological relevance of 3-epi-25(OH)D3 may be related to the 3-epi-25(OH)D3 as a percentage of total 25(OH)D and should be considered in future investigations.