Since the autoimmune nature of type 1 diabetes mellitus came to become known some 40 years ago, continuous investigations have been carried out in an attempt to improve approaches to prognostication of this disease and develop new safe and efficacious methods for its prevention. For all that, many aspects of diabetes pathogenesis still remain far from clear. In most cases (roughly 85%), type 1 diabetes mellitus (DM1) develops sporadically in the absence of a relevant familial or hereditary history of this condition. Accordingly, the first-degree relatives account for only 15% of all DM1 patients. The risk of development of DM1 in the Russian population estimated by the researchers of the Children' Department, Endocrinological Research Centre, is relatively low (0.2%). It depends on many factors, such as the number of ill and healthy relatives, the chronological age of a given patient and the age of onset of clinical manifestations in his (her) relatives. Type 1 diabetes-predisposing and protective haplotypes were identified in the Russian population based on the results of molecular-genetic studies involving 599 children and adolescents with DM1. These and immunological data were used to distinguish between risk groups in the families of diabetic patients and the rationale was proposed for the dynamic follow-up of these subjects. It is concluded that estimation of the risk of type 1 diabetes mellitus based on the results of molecular-genetic studies and monitoring immunological markers constitutes the first step in the elaboration of preventive measures designed to prevent or delay the development of the disease.