Context: Recent in vitroandin vivo experimental evidence supports a role of vitamin D insufficiency as an important factor in the development of uterine leiomyomas. However, epidemiological data supporting this possibility are scanty. Objective: Our objective was to investigate vitamin D status in women with and without uterine leiomyomas. Design: This was a case-control study of women referring to 2 infertility units in Italy. Women were eligible as cases if they were diagnosed with at least 1 uterine leiomyoma with a mean diameter ≥10mmat transvaginal ultrasound. Each of them was matched to the 2 subsequent women of the same age (±1 year) whose uterus resulted unremarkable at ultrasound. Selected women provided a blood sample for the quantitative detection of 25-hydroxyvitamin D3 levels. Main Outcome Measure: We measured serum concentration of 25-hydroxyvitamin D3. Results: Atotal of 128 women with leiomyomas and 256 controls were selected. The mean±SD serum concentration of 25-hydroxyvitamin D3 was significantly lower in affected women compared with controls (18.0 ± 7.7 vs 20.8 ± 11.1 ng/mL respectively, P = .010). The number (proportion) of women with 25-hydroxyvitamin D3 deficiency (ie,