Background: To determine the prevalence of vitamin D deficiency among pregnant mothers and their neonates and to study the effect of vitamin D deficiency on maternal and perinatal outcome.Methods: This prospective cohort study conducted in a teaching hospital included 223 pregnant mothers and their offspring born in 2017. Detailed history was taken to ascertain the causes of vitamin D deficiency. vitamin D3 and calcium levels were estimated in maternal and cord blood samples. To study the association between the vitamin D status and the various maternal and neonatal parameters.Results: 91.9 % of women were house wives involved in indoor activities. Pre-eclampsia and GDM were seen in 4.5% of cases each. 5.41% were obese and 84% were of medium complexion, and 8% were dark. 93.7% were non- vegetarians, and fish, egg and milk consumption was adequate in 61.3% , 64% and 71% respectively. Only 5.40% of women had adequate exposure to sunlight. The mean birth weight was 3.08± 0.36 Kg. and 14 babies were admitted to NICU for neonatal asphyxia.77.40% had deficient levels of vitamin D <20 ng/ml. Only four pregnant mothers (1.8%) had sufficient levels vitamin D. There was no statistically significant association between vitamin D deficiency and various maternal and neonatal parameters.Conclusions: This study has shown that the prevalence of vitamin D deficiency among south Indian pregnant mothers and their newborn is very high and the ways to improve the vitamin D status among pregnant mothers should be looked at.