Summary: It has been well documented that vitamin D deficiency is very common in modern societies and is linked to a wide range of acute and chronic disease, including diabetes. Recent reports have suggested an association between supplementation with vitamin D and improvement in metabolic control of diabetes, particularly type 2. However, whether this association is causally related to low vitamin D status remains to be determined. Data from large, well-controlled clinical trials with vitamin D supplements as an adjuvant in prevention and treatment of diabetes are awaited to settle this issue. The aim of this paper was to briefly present the mechanisms of vitamin D action that are suggested to be responsible for beneficial modification of impaired glucose metabolism.