Goal:To investigate the correlation between TSH and HbA1c in the treatment of L-thyroxine in the process of glycemic control in patients with subclinical hypothyroidism.Patients and methods:The sample consisted of 100 patients, mean age 51.75±3.23 years, BMI=27.97±4.52 kg/m2, with SH (TSH>4.2 mU/L and normal serum T3 and T4). Laboratory diagnosis included the determination of free T3, free T4, thyroid antibodies, Tg, insulin, C-peptide and glucose during the OGTT, HbA1c, CRP and lipid levels. 20 patients with SH had prediabetes and 38 patients had DM. All patients were treated with low doses of L-thyroxine (25-50ug) and all were physically active.Results:After 6 months of treatment with L-thyroxine, the patients had normal or decreased TSH (5.85±0.92 vs. 3.54±0.55 mU/L), insulin levels (114.64±24.11 vs. 96.44±17.26 pmol/L) significantly reduced HbA1c (6.74±1.01 vs. 6.26±1.12) is reduced.Conclusion:The correlation between TSH and HbA1c was positive and significant (r=0.46). This indicates a significant effect of treatment with L-thyroxine on glycemic control in patients with subclinical hypothyroidism.