A community-based study was undertaken in an urban slum in Mumbai, between October, 2015 and September, 2017 among 426 healthy children (aged 1-5 years) to assess prevalence of vitamin D deficiency (VDD) and its determinants. VDD was classified as 25(OH)D <20 ng/mL. The prevalence of VDD was 76.8% (n=327), and sun-exposure, male sex, and calcium and vitamin D supplementations during infancy were important determinants. Routine supplementation with vitamin D in infancy is likely to reduce the occurrence of VDD in children.