Polycystic ovarian syndrome is a common cause of ovarian dysfunction in women with anovulation world wide.50-70% of patients with PCOS exhibit metabolic abnormalities, including poor glucose tolerance and hyperinsulinemia. The prevalence of vitamin D deficiency in women with PCOS is about 67-85 per cent, with serum concentrations of 25(OH) D <20 ng/ml. It is suggested that there is an association between serum levels of vitamin D and metabolic parameters in women with PCOS, including fasting glucose levels, fasting insulin, insulin resistance, high blood pressure, lipid disorders, obesity, fertility and other clinical and laboratory- related parameters associated with PCOS. Given the high prevalence of vitamin D deficiency in the south Indian population, less number of studies, inconclusive studies, especially in the population of women with PCOS, as well as evidence from recent studies indicating a link between vitamin D levels with lab parameters, this study aimed to assess the relationship between vitamin D deficiency and insulin resistance in PCOS. Pearsons correlation showed 0.034 between HOMA IR and vitamin d levels indicating that vitamin d deficiency is associated with more HOMA IR values, the more insulin resistance. Pearsons correlation showed 0.05 between fasting insulin levels and vitamin d levels indicating the vitamin d deficiency is associated with more fasting insulin levels, the more insulin resistance. No significant relation is seen with fasting glucose insulin levels (Pearsons correlation value >0.05). In the study, it was found that a high percentage of PCOS women were vitamin D deficient. The study also showed a significant difference in the values of some clinical and metabolic parameters such as waist circumference, fasting insulin, HOMA-IR, BMI between PCOS women with and without vitamin D deficiency; however, no linear correlation was found between serum levels of vitamin D and baseline variables, except for HOMA IR values, fasting insulin levels, BMI, G120. In conclusion, our data confirm an association between vitamin D deficiency and Insulin resistance in patients with PCOS. Thus, vitamin D supplementation could be a beneficial treatment of PCOS women to abolish insulin resistance and regulate menstrual irregularities.