Abstract Background: Type 1 diabetes Mellitus is a result of the autoimmune destruction of beta cells leading to insulin defi-ciency. Vitamin D deficiency may have a role in the develop-ment and pathogenesis of type-1 diabetes Mellitus by modu-lating immune mechanisms. Aim of Study: Our study is a cross-sectional study aimed to assess the level of 25-hydroxy vitamin D in children with type 1 diabetes Mellitus. Patients and Methods: Eighty patients attending the endocrinology clinic in the period from November 2016 to August 2017 were included, their ages ranged from 5 years to 15 years and all patients proved as having type 1 diabetes mellitus and were on insulin therapy. All patients were sub-jected to full history taking, and clinical examination in addition to the assessment of vitamin D status with measuring of serum 25-hydroxyvitamin D level in a venous blood sample. Results: The incidence of type 1 diabetes was greater in females (65%) than in males (35%). Ages between 10-15 years were more commonly affected than the younger age group (5-10) years. Higher rates were recorded in urban than rural areas. 40% of studied children with type 1 diabetes had vitamin D deficiency but 60% of them had a sufficient level of vitamin D. Vitamin D insufficiency with type 1 DM was more common in females (83.9%), in age group (10-15) years (74%), in urban population (67%) and in children with daily consumption of junk food (64.50%). Type 1 diabetic children with vitamin D insufficiency were more liable to frequent infections and hospital admission (90%). Conclusion: Our study concludes that vitamin D deficiency was significantly detected in type 1 diabetic children. In addition, vitamin D deficiency in these patients is associated with frequent hospital admission and complications.