Objective. To examine the prevalence and correlates of vitamin D deficiency and inadequacy among US women of childbearing age. Methods. Data from 1,814 female participants (20-44 y) in the 2003-2006 NHANES were analyzed to estimate the age-adjusted prevalence and prevalence ratios with 95% confidence intervals (CIs) for vitamin D deficiency (defined as serum 25-hydroxyvitamin D [25(OH)D] <12.0 ng/mL) and inadequacy (defined as 25(OH)D: 12.0-<20.0 ng/mL). Results. The age-adjusted prevalence was 11.1% (95% CI: 8.8-14.0%) for vitamin D deficiency and 25.7% (95% CI: 22.3-29.5%) for vitamin D inadequacy. Race/ethnicity other than non-Hispanic white and obesity were associated with increased risks, whereas dietary supplement use, milk consumption of ≥1 time/day, and potential sunlight exposure during May-October were associated with decreased risks for both vitamin D deficiency and inadequacy (P < 0.05). Current smoking and having histories of diabetes and cardiovascular disease were also associated with an increased risk for vitamin D deficiency (P < 0.05). Conclusions. Among women of childbearing age, periconceptional intervention programs may focus on multiple risk factors for vitamin D deficiency and inadequacy to ultimately improve their vitamin D nutrition.