OBJECTIVES: To identify how children and adolescents with type 1 diabetes were coping with their condition during the COVID-19 lockdown, by detecting differences in blood glucose control and in lifestyle, including diet, physical activity, and mood deterioration, before and during the lockdown. METHODS: This descriptive, cross-sectional study was conducted between April and June 2020 at King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia. Data were collected from interviews, using various forms of telecommunication. RESULTS: The total sample size was 150 patients, 48 (28%) of whom were males and 102 (72%) females. The mean age of the patients was 12.45 years. The lockdown was associated with a significant increase in patients' weight (p=0.001), body mass index (p=0.001), and blood glucose readings (p=0.007) compared to their values before the lockdown. Conclusion: A negative impact of the COVID-19 lockdown was found on blood glucose values and BMI, which may correlate with a lack of physical activity, increased consumption of carbohydrates and fast food, and mood deterioration.