Vitamin D is the third steroid hormone playing important bio-logical roles in the development of breast cancer. Decreased plasma levels of its 25- hydroxyderivative, 25OHD, display robust associations with higher incidence of breast cancer and shorter overall survival. Although no consensus exists, most authors agree that optimal plasma levels shall be within 75- 150 nmol/ l whereas levels higher than 375 nmol/ l can be potentially toxic with higher risk of hypercalcemia. To date, no data are available on the optimal levels of vitamin D related to the risk of breast cancer development, its phenotype features and the course of the disease. Published studies mostly describe associations among higher levels of 25OHD and lower bio-logically aggressiveness of the tumor. The polymorphism of VDR gene coding for the steroid receptor for vitamin Dmay be associated with higher disease incidence and also be of negative prognostic significance in breast cancer. This review presents an overall summary of the current knowledge and publications on vitamin D and breast cancer.