CONTEXT: An inverse relationship between total serum 25-hydroxyvitamin D (25-OH D) and increased adiposity has been established in children, adolescents, and adults. However, the relationship between neonatal adiposity and vitamin D status has not been reported. Both maternal obesity and vitamin D deficiency in pregnancy are common and are associated with adverse pregnancy outcomes. OBJECTIVE: The aim of the study was to determine the relationship between vitamin D levels in mothers and newborns, as influenced by maternal obesity, and evaluate these associations with neonatal adiposity. DESIGN, SETTING, AND PATIENTS: Sixty-one maternal-neonatal pairs participated in this cross-sectional study at an academic medical center. Mothers had a prepregnancy body mass index that was normal or obese. OUTCOME MEASURES: Maternal and cord blood sera were assayed for 25-OH D, and neonatal body composition was measured by air displacement plethysmography. RESULTS: Mothers had similar and sufficient levels of 25-OH D when measured at 36-38 wk gestation, irrespective of body mass index category (normal weight, 46.05, vs. obese, 49.84 ng/ml; P = not significant). However, cord blood 25-OH D was higher in neonates of normal-weight mothers compared to neonates of obese mothers (27.45 vs. 20.81 ng/ml; P = 0.02). The variance in cord blood 25-OH D was explained by four factors: maternal 25-OH D level, the presence of maternal obesity, maternal age, and neonatal adiposity (r(2) = 0.66). CONCLUSION: Obese women transfer less 25-OH D to offspring than normal-weight women, despite similar serum levels. Cord blood 25-OH D levels directly correlate to neonatal percentage body fat. These novel findings underscore the evolving relationships between maternal obesity, vitamin D nutritional status, and adiposity in the neonatal period that may influence subsequent childhood and adulthood vitamin D-dependent processes.