17 Background: Bone health is a particular concern for breast cancer survivors, because these women have 15% higher fracture risk than women without a history of breast cancer. Many studies have suggested that vitamin D deficiency may be involved in breast cancer initiation, progression, and prognosis. This study examines the prevalence of vitamin D deficiency among postmenopausal breast cancer patients in minority population. METHODS This retrospective study reviewed the electronic records of 200 postmenopausal breast cancer patients from ethnic groups of blacks, Hispanics and Asians. RESULTS Of the 200 patients, 84 (42%) had their 25-OHD levels checked at least once. Of patients, 42.7% found body mass index (BMI)>30kg/m2. There was significant difference between race and BMI (p<0.05). Black Vitamin D deficiency (level< 20ng/mL) found in 35 (41.7%), vitamin D insufficiency (level range 20-30ng/mL) found in 30 (35.7%) of the patients. The median serum 25-OHD level was 21 (range 4-65ng/ml). The serum 25-OHD levels did not have significant difference among blacks and Hispanics. Tumor stages found negatively correlated with 25-OHD levels r=-0.227 and p=0.04. CONCLUSIONS This study revealed that vitamin D deficiency has a high prevalence among postmenopausal breast cancer minority population. Data from Third National Health and Nutrition Examination survey showed that mean serum 25-OHD levels among white, Hispanic and black women were 76ng/ml, 56.7ng/ml and 45.3ng/ml, respectively. Also, prevalence rate of vitamin D deficiency is reported in the studies among breast cancer patients are approximately 30%. Our data compared with this general population's numbers is low; our median 25-OHD level was 21ng/ml. Our study found negative correlation with Vitamin D levels and stages of the breast cancer. Information is lacking on direct prognostic effect of vitamin D in breast cancer but this findings including our study support the hypothesis that vitamin D has a role in the pathogenesis of breast cancer. In the setting of breast cancer diagnosis either for bone health, or for breast cancer prognosis in postmenopausal women, we advocate routine 25-OHD levels screening for the vitamin D deficiency especially in minority populations would be beneficial.