Insulin autoantibodies (IAA) represent the major serological marker of type 1 diabetes mellitus (T1D), the disease resulting from autoimmune damage to β-cells in the pancreatic islets. Testing for IAA is used in early and differential diagnosis of T1D, as well as to perform screening for this disorder. The best foreign diagnostic labs perform IAA tests using different radioimmunoassay (RIA) formats. The RIA operational parameters, i. e. diagnostic sensitivity (DSe), diagnostic specificity (DSp), and diagnostic accuracy (DA), are on average equal to 44%, 100%, and 81%, respectively. Unfortunately, in Russia RIA has not been used to determine IAA for a long time. All Russian labs use the enzyme-linked immunoassay (ELISA)-based test systems for this purpose. DSe, DSp, and DA of ELISA systems are on average 24%, 87%, and 62%, respectively, i.e. considerably lower compared to RIA systems. Our study aimed to reproduce IAA RIA in the diagnostic lab of the RCCH. The method is based on IAA competitive binding to insulin and ¹²⁵I-labeled insulin. Serum samples from patients with new onset T1D and patients without diabetes were tested for IAA. DSe, DSp, and DA were 43%, 100%, and 73%, respectively. Thus, the operational parameters of the reproduced IAA RIA reproduced are close to the parameters of the RIA-based methods used in foreign labs and are significantly superior to the parameters of the ELISA-based tests.