Background: Vitamin D has multiple effects on innate and adaptive immune responses .It was found that low vitamin D levels are associated with many autoimmune diseases .The relation between vitamin D levels and alopecia areata ( a tissue-specific autoimmune disease of hair follicles) represents an attractive area of research. Purpose: To estimate the serum level of 25 hydroxy vitamin D in patients with alopecia areata and detect any possible relation between vitamin D level and the development of alopecia areata. Patients and methods: This study recruited 70 patients with alopecia areata and 70 age- and sex-matched healthy control subjects. Levels of serum 25 hydroxy vitamin D were estimated by ELISA technique. The correlations between serum 25 hydroxy vitamin D levels and age, sex, adequacy of sun exposure, duration of disease and severity of alopecia areata were assessed. Results: Serum 25 hydroxy vitamin D levels were significantly decreased in the alopecia areata group (mean±SD=66.4±32.6) compared with the control group (mean±SD=84.2±55.9) (P = 0.023). Female subjects in both groups (patients and controls) showed highly significant lower vitamin D levels than males (P=0.005). No significant difference in the level of 25 OH vitamin D was found in patients experienced adequate or inadequate sun exposure. There was no positive correlation between serum 25 hydroxy vitamin D levels and family history, severity and duration of AA, or between serum 25 OH vitamin D level and age of patients and controls. Conclusions: Low levels of 25 hydroxy vitamin D are associated with alopecia areata. More studies are required to prove that low levels of vitamin D are a causative factor or an outcome of the disease.