Vitamin D is an endogenous product of mammalian organisms from which an active agent of a steroid hormone nature is synthesized. These hormones participate in a variety of key metabolic processes in every nuclear cell, whether on endocrine, paracrine and autocrine or subcellular level. Vitamin D represents a very interesting molecule which participates in a great deal of body processes. This review summarizes the findings about the metabolism of vitamin D focusing on pathophysiology of malignant diseases.