question: BACKGROUND In order to limit the spread of COVID-19, governments have ordered a series of restrictions that may affect glycemic control in individuals with T1DM, since physical activity (PA) was not allowed outside home. MATERIALS AND METHODS We retrospectively evaluated glycemic control of individuals with T1DM using HCL system in the period before the SARS-CoV-2 outbreak in Italy (February 10th - 23rd, 2020 - Time 1), when movements were only reduced (February 24th - March 8th, 2020 - Time 2) and during complete lockdown (March 9th-22nd, 2020 - Time 3). Information about regular PA (at least 3 hours per week) prior and during the quarantine were collected. RESULTS The study included 13 individuals with a median age of 14.2 years and a good glycemic control at baseline (GMI 7%, TIR 68%, TBR 2%). All individuals continued to show good glycemic control throughout the study period. There was an increase in TIR during the study period (+3%) and TIR was significantly higher in Time 3 (72%) than in Time 2 (66%). TBR was significantly lower in Time 3 (1%) both compared to Time 1 and Time 2 (2%). A meaningful variance in TIR at Time 3 between individuals who performed or not PA during quarantine and a significant increase in TIR between Time 2 and Time 3 both in individuals doing PA at baseline and during quarantine, was found. At logistic regression, only the presence of PA during quarantine significantly predicted a TIR >70 %. CONCLUSIONS Glycemic control of T1DM in adolescents using HCL system did not worsen during the restrictions due to COVID-19 pandemics and further improved in those who continued physical activity during the quarantine. Maintaining regular physical activity in a safe home environment is an essential strategy for young individuals with T1DM during the COVID-19 crisis.