Aim. To study the time course changes in the parameters of endothelial dysfunction in patients with type 2 diabetes mellitus (DM) and subclinical hypothyroidism (SH) in the natural course of SH and during replacement therapy. Subjects and methods. All the examined patients were divided into 2 groups: 1) 67 patients received replacement therapy with euthyrox in a dose of 25 to 100 µg/day; 2) 60 patients were followed up. Results. At the moment of study inclusion, there was a close direct correlation between the levels of cholesterol and the aggregate intima-media thickness (IMT) (r=0.7) and between IMT and the levels of sICAM-1 (r=0.71) and sVCAM-1 (r=0.8). In the dynamics of the disease (following a year), the above correlations became weaker due to the performed treatment. A weak positive correlation was found between the aggregate IMT and the levels of sICAM-1 (r=0.2) and sVCAM-1 (r=0.3). Conclusion. In patients with type 2 DM, the presence of SH serves as an additional risk factor for endothelial dysfunction. Replacement therapy will be able to considerably retard the progression of the disease and to reduce the incidence of vascular events.