Vitamin D is a vitamin not only associated with calcium-phosphorus metabolism but also affects many organ systems. Because of its effect on the immune system in recent years, it has attracted much attention. Vitamin D deficiency is a clinical condition that can be widely observed in the society. Thus, patients with vitamin D deficiency are often seen in anaesthesia practice. In the absence of vitamin D, prolongation of intensive care unit stay, increase in mortality and morbidity and also association of chronic diseases further increase the importance of vitamin D deficiency. The results obtained from studies have led to the question of whether poor surgical outcome is associated with vitamin D deficiency. We assessed the vitamin D deficiency and its negative consequences for the anaesthesiologist.