BACKGROUND : Low maternal vitamin D status has been associated with several adverse outcomes during pregnancy. The aim of the study was to evaluate the vitamin D levels in preeclamptic and healthy pregnant women and the role of vitamin D deficiency in the etiology of preeclampsia. METHODS : In this case-control study, 80 preeclamptic women and 80 healthy pregnant women were selected from Motahari hospital in Urmia, Iran. 2 ml of venous blood sample was collected from each pregnant woman and the serum 25-OH-D level was measured by Enzyme-Linked Immunosorbent Assay (ELISA) and reported in nanograms per milliliter. levels of 25-OH-D less than 10 ng mL-1, between 10 ng mL-1 and 29 ng mL-1 and more than 30 ng mL-1, were considered as deficient, insufficient and normal 25-OH-D concentrations, respectively. Results were analyzed by independent t-test, Mann-Whitney U test, and logistic regression. RESULTS : Preeclamptic women (n = 80) were noted to have decreased total 25-OH-D levels relative to healthy control women (n = 80; P = 0.01). This difference in total 25-OH-D remained significant after control for potential confounders [odds ratio (OR) = 4.79, confidence interval (CI) = 1.45-9.87, P = 0.01]. CONCLUSIONS : These results showed that vitamin D deficiency has a statistically significant relationship with preeclampsia and support the hypothesis that vitamin D deficiency may be a risk factor for preeclampsia.