Aim: To assess the long-term efficacy of an advanced hybrid closed loop (aHCL) system and to identify clinical characteristics of people with Type 1 Diabetes Mellitus (T1DM) improving their Time In Range (TIR) due to aHCL system therapy. Materials and methods: This was a retrospective observational study conducted on 77 patients with T1DM (33.8% males, mean age 46.9±13.7 years, mean disease duration 28.6±12.8 years) followed-up at Niguarda Hospital, Milan, using aHCL therapy. In addition to demographic data and clinical characteristics, sensor metrics and indices of glycemic variability were analyzed at baseline and at the last available follow-up. The entire study sample was divided into two groups based on the magnitude of improvement in TIR between baseline and the end of observation (Delta TIR): Group 1 with Delta TIR >10% and Group 2 with delta TIR<10%. Results: In a median follow-up of 2.0 years (min. 0.62 years; max. 2.9 years) statistically significant improvement was observed in HbA1c (-0.62%±1,06%; p<0.0001), TIR (+4.77%±11.92%; p=0.002) TAR 181-250 mg/dl (-3.17%±8.67%; p=0.005), TBR 70-54 mg/dl (-0.38%±1.32%; p=0.024), TBR<54 mg/dl (-0.20%±0.73%; p<0.036), compared to baseline. Patients achieving an improvement of TIR >10% (Group 1; 36%) showed, at baseline, statistically higher HbA1c (8.0%±0.9% vs 7.3%±1.3%; p=0.045), mean blood glucose (163.1±19.1 mg/dl vs 147.2±19.3 mg/dl; p=0.004), standard deviation (55.5±9.7 mg/dl vs 48.4±9.4 mg/dl; p=0.008), J index (48.4±12.0 mg/dl2 vs 38.9±11.1 mg/dl2; p=0.004), CONGA4 (74.7±12.5 mg/dl vs 67.3±11.9 mg/dl; p=0.03), MODD (54.2±11.7 mg/dl vs 48.4±9.3 mg/dl; p=0.04), HBGI (7.4±3.0 vs 5.1±2.9; p=0.005), BGRI (8.1±2.8 vs 5.8±2.7; p=0.004), compared to patients in Group 2. Conclusion: The advanced hybrid closed loop system proved to be effective in a long-term follow-up. Baseline clinical characteristics may be useful in order to better identify patients who can benefit most from aHCL therapy.