<p> Objective: To study the prevalence of Vitamin D deficiency by assessing 25(OH) Vitamin D levels in children with Down syndrome and to assess its effect on height, bone age and other related biochemical markers (calcium, phosphorus and alkaline phosphatase). Methods: This was a prospective study in a tertiary care hospital in South India where consecutive children with Down syndrome between the ages of 5 months - 16 years seen over one year were included. The height, weight (and head circumference of children less than 3 years) were plotted on growth charts for Indian children (Indian Academy of Pediatrics) and for children with Down syndrome as described by Cronk. Results: Fifty six children with Down syndrome were enrolled. Prevalence of 25(OH) vitamin D deficiency using a cut off value of 10 ng/ml was 26.8%. There was no significant effect of 25 (OH) Vitamin D deficiency on height (p = 0.26) and bone age (p = 0.3). The independent samples T test showed no difference in the values of serum calcium, phosphorus and alkaline phosphatase in children with 25 (OH) Vitamin D levels < 10ng/ ml and >= 10ng/ml. Conclusion: There was no significant effect of vitamin D deficiency on height, bone age and other associated biochemical markers in these children.</p>