Abstract Background: Several factors have been implicated in causing low levels of vitamin D, which is an important hormone regulating the calcium homeostasis in the body. Aim of Study: To assess vitamin D status in Egyptian infants and children from age of 6 months up to age of 5 years and to assess if there is seasonal variation in its level. Patients and Methods: The present study was conducted as a cross section study included infants and children aged 6 months up to 5 years attending the outpatient clinic of Man-soura University Children Hospital, 100 of them were taken during winter time and 100 during summer time. Each child underwent: Full history taking, thorough clinical examination, laboratory investigations and assessment of Vitamin D. Results: 33.5% of the total studied children had vitamin D deficiency <20ng/ml) and 41.5% had vitamin D insufficiency (³20ng/ml-<30ng/ml). The median of serum vitamin D was (54.5ng/ml) in the summer group which was significantly increased than its level in the winter group (23.7ng/ml) (p-value=0.001). Winter season and absence of sun exposure had significant risk of developing vitamin D deficiency or insufficiency (p-value=0.001). Conclusion: High prevalence of vitamin D deficiency in apparently healthy Egyptian children was observed in this study. There was a significant relationship between vitamin D status of the children and both of seasonal variations and sun exposure which reflects that sun exposure play a vital role in the synthesis of this vitamin and vitamin D status in children.