Objective Vitamin D deficiency has been linked to adverse pregnancy outcomes. The purpose of this investigation was to assess total 25-hydroxyvitamin D (25-OH-D) levels at diagnosis of early-onset severe preeclampsia (EOSPE). Study Design After institutional review board approval, we enrolled subjects with EOSPE (<34 weeks' gestation with severe preeclampsia) in this case-control investigation in a 1:2 ratio with gestation-matched, contemporaneous control subjects. Demographic and outcome information was collected for each subject. Plasma total 25-OH-D levels were determined by radioimmunoassay and reported in nanograms per milliliter. Results were analyzed by Mann-Whitney U and multivariable regression. Results Subjects with EOSPE (n = 50) were noted to have decreased total 25-OH-D levels relative to healthy control subjects (n = 100; P < .001). This difference in total 25-OH-D remained significant after control for potential confounders. Conclusion Total 25-OH-D is decreased at diagnosis of EOSPE. Further study is needed to understand the impact of vitamin D deficiency on pregnancy outcomes.