Vitamin D deficiency is a major health problem worldwide in all ages. Low vitamin D levels is a problem even in countries with sun exposure all year around. This problem particularly high in Middle East, especially among women. Inter individual variability of serum vitamin D concentrations caused by behavioral, environmental factors and contribution of genetic component. In addition, polycystic ovary syndrome is a common heath problem affects about 5 to 10 % of reproductive age women. This book, therefore, aimed to assess serum 25-hydroxy vitamin D3 levels in women with polycystic ovary syndrome and compare their levels with age and body mass index matched healthy controls. Also, Cdx2 (G/A) single nucleotide polymorphism of vitamin D receptor gene was examined among women with polycystic ovary syndrome and controls and tested for its effect on vitamin D levels and/or polycystic ovary syndrome susceptibility.