This draft clinical practice guideline for the diagnosis, treatment and prevention of vitamin D deficiency is an update from a previous 2016 document. An analysis of the relevant literature data was carried out, with particular attention to meta-analyzes, randomized clinical trials and systematic reviews published over the past 5 years. The updated recommendations were discussed and revised by the leading endocrinologists of the Russian Federation, who have expert status in this issue.The classification of 25(OH)D levels has been revised (in particular, the target range of 25(OH)D values has been specified), recommendations have been developed for screening of the disorders associated with vitamin D deficiency. The concept of vitamin D-associated toxicity and recommendations for its diagnosis and prevention have been introduced. Also, indications for the assessment of other vitamin D metabolites besides 25(OH)D, the main marker of vitamin D status, have been indicated.The section regarding treatment of vitamin D deficiency has been expanded and corrected. The major additions concerned the replenishment of the vitamin D deficiency and insufficiency in certain categories of patients (particularly, in the presence of the chronic kidney disease and autoimmune diseases, as well as in pregnant women) and monitoring of the effectiveness and safety of the therapy. The indications for prescribing active metabolites of vitamin D have been adjusted. Recommendations for the prevention of vitamin D deficiency in the general population have also been revised, taking into account large randomized clinical trials, meta-analyzes and systematic reviews of recent years.This publication is an expanded version of the federal guidelines.