Background: Maintenance of stable glycemic control is an important prerequisite of effective treatment of patients with type 1 diabetes mellitus (DM). The ultra-long-acting basal insulin degludec allows for reduction of glycemic variability and for a substantial reduction in the rates of hypoglycemia with equivalent glycemic control. Evaluation of the impact of this novel insulin on diabetes-dependent quality of life and patient satisfactions with the treatment is necessary for comprehensive assessment of treatment efficacy.Aim: To study changes of glycated hemoglobin (HbA1c), rates of hypoglycemia, diabetes-dependent quality of life and treatment satisfaction in patients with type 1 DM, who have been switched to insulin degludec.Materials and methods: This open 12-week observational comparative study included 25 patients with type 1 DM (median age, 36 [20; 63] years), who were switched to insulin degludec in combination with a ultra-short insulin analogue. The control group included 21 patients with type 1 DM (median age, 40 [23; 63] years), who continued their treatment with a long-acting insulin analogue glargine. At baseline and at week 12 after switching to insulin degludec, we assessed HbA1c level, mean insulin dose, depression score, diabetes-dependent quality of life and patient satisfaction with the treatment with the use of the Russian versions of the diabetes-specific questionnaires “Audit of Diabetes-Dependent Quality of life” (RuADDQoL), and “Diabetes Treatment Satisfaction Questionnaire” (DTSQ), respectively.Results: At 3 months, there was a significant reduction of the HbA1c levels in the main and the control groups to 7.57% (Ме 7.5 [7.1; 8.4]; р=0.03) and 8.18% (Ме 7.8% [7.4; 8.7]; р=0.04), respectively. The mean reduction of this parameter under treatment with degludec was slightly higher than under treatment with glargine (0.73 vs 0.57%, respectively), at 3 months the difference being statistically significant (p=0.034). To achieve an equivalent glycemic control, the mean daily dose of insulin degludec was reduced by 26%. Switching to insulin degludec was associated with a significant reduction in non-severe hypoglycemia rates by 45% (р<0.001). In the main group, there was an improvement of the mean total weighted score of Ru-ADDQoL from -2.2 (Ме -1.28 [-2; -0.86]) at baseline to -1.5 (Ме -1.28 [-2; -0.86]) at 12 week, with positive changes in the most domains, demonstrating the improvement of quality of life In the reference group, the mean total weighted Ru-ADDQoL score at 3 months increased 0.4 (Me 0.1 [-0.56; -1] to -1.51 (Me -1.23 [-2; -1]). In the glargine group there were no significant changes on any of the Ru-ADDQoL domains. There was a significant improvement in the patients satisfaction with treatment in the degludec group, with an increase of the average DTSQ score by 5 in 3 months of therapy.Conclusion: Based on the results of this short-term observational study, the following conclusion can be drawn: treatment with insulin degludec in type 1 DM is as effective as treatment with insulin glargine; however, it allows for reduction of the mild hypoglycemia rates by 45%. Therefore, this insulin can be recommended, first of all, to those type 1 DM patients who demonstrate substantial glycemic fluctuations, frequent hypoglycemia, hypoglycemic unawareness or who do not achieve the glycemic goals of treatment. Finally, this would lead to better health-related quality of life and more treatment satisfaction.