Many factors have been claimed to increase breast cancer risk; as age at menarche and menopause, hormonal exposures, previous benign breast lesions, family history of breast cancer, exposure to ionizing radiation, smoking and alcohol. Researches claimed vitamin D deficiency as the cause of multiple diseases, including cancer. Perhaps its deficiency upregulates the hormonal and genetic predisposition of the patients and there is still a need for investigating more factors for breast cancer etiology and therapy. Sources of vitamin D are sunlight exposure or diet and dietary supplements. The aim of this study was to demonstrate vitamin D status in breast cancer patients at diagnosis, and weather this level changed with chemotherapy and radiotherapy. This case control prospective study was carried out on 40 premenopausal patients diagnosed as breast cancer patients and 20 healthy women in whom serum hydroxy vitamin D (25OHD) levels were analyzed at the beginning of study, and after chemotherapy and radiotherapy. The data revealed that mean serum vitamin D concentration in healthy control group was (22.35 ± 5.92 ng/ml), which considered insufficient. Patients at diagnosis were vitamin D deficient with mean level (16.77±1.96 ng/ml); then after receiving adjuvant therapy in the form of chemotherapy and radiotherapy, vitamin D mean level was (11.70±3.08 ng/ml); i.e. the mean level decrease by 30.23%. It could be concluded that breast cancer patients had lower vitamin D levels than the age matched control women. Vitamin D in breast cancer patients decreased more after chemotherapy and radiotherapy.