Background: Knowledge gaps have contributed to considerable variation (between 0 and 15 mu g/d) in international dietary recommendations for vitamin D in adolescents.Objective: We aimed to establish the distribution of dietary vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above several proposed cutoffs (25, 37.5, 40, and 50 nmol/L) during wintertime in adolescent white girls.Design: Data (baseline and 6 mo) from 2 randomized, placebo-controlled, double-blind, 12-mo intervention studies in Danish (55 degrees N) and Finnish (60 degrees N) girls (n = 144; mean age: 11.3 y; mean vitamin D intake: 3.7 mu g/d) at vitamin D-3 supplementation amounts of 0, 5, and 10 mu g/d were used. Serum 25(OH) D was measured with an HPLC assay in a centralized laboratory.Results: Clear dose-related increments (P < 0.0001) in serum 25(OH)D with increasing supplemental vitamin D-3 were observed. The slope of the relation between vitamin D intake and serum 25(OH)D at the end of winter was 2.43 nmol . L-1 . mu g intake(-1), and no difference in the slopes between Finnish and Danish girls was observed. The vitamin D intakes that maintained serum 25(OH)D concentrations at > 25, > 37.5, and > 50 nmol/L in 97.5% of the sample were 8.3, 13.5, and 18.6 mu g/d, respectively, whereas an intake of 6.3 mu g/d maintained a serum 25(OH)D concentration > 40 nmol/L in 50% of the sample.Conclusion: The vitamin D intakes required to ensure that adequate vitamin D status [defined variably as serum 25(OH)D > 25 and > 50 nmol/L] is maintained during winter in the vast majority (. 97.5%) of adolescent girls (mean age: 11.3 y) at northern latitudes (> 55 degrees N) are 8.3 and 18.6 mu g/d, respectively. This trial was registered at clinicaltrials.gov as NCT00267540. Am J Clin Nutr 2011; 93: 549-55.