It is estimated that over one billion of people around the globe have low serum values of vitamin D, therefore, we can consider vitamin D deficiency as a pandemic and public health problem. Geographic position of Croatia, especially the continental part of the country, is a risk factor for the development of deficiency of vitamin D in the population. The aim of these guidelines is to provide the clinicians with easy and comprehensive tool for prevention, detection and therapy of vitamin D deficienney in healthy population and various groups of patients. They were made as a result of collaboration of clinicians of different backgrounds who are dealing with patients at risk of vitamin D deficiency. These guidelines are evi- dence-based, according to GRADE-system (Grading of Recommendations, Assessment, Development and Evaluation), which describes the level of evidence and strength of recommendation. The main conclusions address the recommended serum vitamin D values in the population which should be between 75 and 125 nmol/L and defining recommended preven- tive and therapeutic dosages of vitamin D in order to reach the adequate levels of serum vitamin