In utero or early-life vitamin D deficiency is associated with skeletal problems, type 1 diabetes, and schizophrenia, but the prevalence of vitamin D deficiency in U.S. pregnant women has not been investigated. The authors sought to assess vitamin D status of pregnant women and their neonates residing in Pittsburgh by race and season. Serum 25-hydroxyvitamin D (25(OH)D) was measured at 4 to 21 weeks gestation and predelivery in 200 white and 200 African-American pregnant women and in the cord blood of their neonates. Over 90% of women used prenatal vitamins. Women and neonates were classified as vitamin D deficient, insufficient, or sufficient. Vitamin D deficiency and insufficiency occurred in 29.2% and 54.1% of African-American women and 45.6% and 46.8% of African-American neonates, respectively, at delivery. Five percent and 42.1% of white women and 9.7% and 56.4% of white neonates were vitamin D deficient and insufficient, respectively. Findings were similar at less than 22 weeks gestation. African-American women had a smaller mean increase in maternal 25(OH)D compared with white women from winter to summer and from spring to summer after adjustments were made for prepregnancy body mass index and prenatal vitamin use (P<0.01). These results suggest that African-American and white pregnant women and neonates residing in the northern United States are at high risk of vitamin D insufficiency, even when mothers are compliant with prenatal vitamin supplementation. Higher-dose supplementation is needed to improve maternal and neonatal vitamin D nutrition.