Background: Vitamin D is important for bone health. Young adults with type 1 diabetes are reported to have a lower peak bone mass than healthy individuals, which could possibly lead to an increased fracture risk in the future. Thus, optimal supply of vitamin D may be of particular importance for bone health in children and adolescents with T1DM.Objective: To assess the prevalence of vitamin D deficiency in type 1 diabetic (T1DM) adolescents in Diabetic Endocrine Metabolic Pediatric Unit (DEMPU).Methods: In present cross-sectional study we evaluated 30 Egyptian adolescents with T1DM clinically by full history taking and thorough clinical examination. Full history includes; duration of diabetes, residence and sun exposure, type of diet especially low-fat diet and the intake of diet rich in vitamin D, life style and exercise in addition to the presence of bony aches or fractures. Thorough clinical examination laying stress on the anthropometric measurements (Wt.SDS, Ht.SDS, BMI), early signs of puberty and signs of associated disorders &/or diabetes complications. The records of the patients reviewed especially for the mean of HbA1c done in the last year.We measured serum 25-hydroxy-vitamin D, intact parathormone (iPTH), calcium in serum & diet, phosphate, and alkaline phosphatase.Results: The mean of serum vitamin D was 38.59+27.77ng/ml (low level). Despite the high prevalence of vitamin D deficiency, we found a low prevalence of secondary hyperparathyroidism (13%) in vitamin D deficient adolescents. There was positive significant correlation between serum vitamin D and serum phosphorus (p value=0.015) and serum parathormone (p value=0.045). Furthermore, there was no significance correlation between serum vitamin D and (anthropometric measures, duration of diabetes, serum parathormone, serum phosphorus, HbA1C%, insulin dose, sun exposure, exercise, vitamin D in diet, calcium in diet and Kcal in diet).Conclusion: Prevalence of vitamin D deficiency in diabetic children is relatively high. Therefore, screening for vitamin D deficiency and supplementation of children with low vitamin D levels should be warranted.