The results of studies carried out in recent decades in different countries of the world indicate an increase in the prevalence of vitamin B12 deficiency including its subclinical form which is the basis for searching for new approaches to the diagnosis and treatment of B12-deficiency conditions. The article discusses the features of the pharmacokinetics and pharmacodynamics of vitamin B12, the causes and risk factors for the development and clinical manifestations of its deficiency; also, it provides the modern recommendations for screening and diagnosis of vitamin B12 deficiency. It’s under discussion the usage of oral preparations contain-ing 1000 μg of cyanocobalamin which has a number of advantages over intramuscular injections from the point of evidence-based medicine. © 2021, Media Sphera Publishing Group. All rights reserved.