▪ Adolescents with T1DM showed significantly higher BMI compared to the control group.▪ Physical activity level showed no association with adolescents’ socioeconomic position, HbA1c levels, or the method of insulin delivery.▪ BMI was negatively associated with physical activity during lockdown.▪ All participants showed reduced physical activity during lockdown; rates did not differ between the T1DM and control group, nor between males and females. The gene discussed is INS; the disease is type 1 diabetes mellitus.