Introduction: Besides its role in calcium homeostasis, vitamin D (VD) has an important immune mudulation effect. However, its role in autoimmune diseases such as type 1 diabetes is under discussion. In this study, we aimed to assess VD status in children and adolescents with type 1 diabetes mellitus (T1DM). Material and Methods: This is a retrospective descriptive study realized at the endocrinology–diabetology department of OUJDA’s Mohammed VI university hospital, included 120 type 1 diabetics under the age of 19 years, with evaluation of vitamin D status. Results: The sex ratio in our study was 1.2 (M/F) with a mean age of 13.4 ± 4.15 years. 32.2% have a history of type 1 diabetes mellitus over 5 years. The mean HbA1c was10.97 ± 2.42 %. Of 120 of cases with T1DM, most had inadequate levels of vitamin D: sufficiency, 3.3% (n = 4); insufficiency, 75 % (n = 90); deficiency, 21.7% (n = 26). In bivariante analyses for age, sex, visit season, z–BMI, diabetes duration, and A1c, age was most significantly associated with the level of 25OHD (P < 0.037, r –, 191*); older age was associated with lower 25OHD concentrations. Discussion and conclusion: Previous studies have shown that the early years of adolescence are often associated with a rapid decline in vitamin D. Because of many risk factors that may not be modifiable due to the inherent presence of diabetes mellitus, vitamin D deficiency during childhood and during the period of peak bone mineral accumulation in this population is justified.