We aimed to evaluate the glycemic effect and detect any predictors of improved time-in-range (TIR) in persons with type 1 diabetes after initiating hybrid closed-loop (HCL) treatment with MiniMed 670G in a 12-month retrospective observational study. Before starting HCL treatment, the 62 participants followed a Steno-developed training program; 7 participants (6.5%) discontinued the HCL therapy; the remaining 55 (58% female) had an age (mean +/- standard deviation) of 45.6 +/- 12.6 years and diabetes duration of 28.2 +/- 10.9 years. After 12 months' HCL therapy, glycated hemoglobin A1c decreased from 7.4% +0.7% to 7.1% +0.5%, TIR increased from 59.3% +/- 13.5% to 72% +/- 9.3%, time in 54-70 mg/dL (3.0-3.9 mM) decreased from 2.4% +/- 2.0% to 1.4% +/- 1.0%, and time in 180-250 mg/dL (10.0-13.9 mM) decreased from 26.4% +/- 8.3% to 20.8% +/- 5.5%, all P < 0.001. Improvement in TIR was significantly associated with lower total daily insulin dose, higher amount of total carbohydrate, and more time spent in Auto Mode. Our findings support the promising results on glycemic outcomes seen with HCL treatment.