Objective: To test the hypothesis whether low levels of serum vitamin D and high levels of parathyroid hormone is associated with elevated BMI. Material & Methods: This study was carried out in the Department of Biochemistry, BMSI, JPMC, Karachi. Total 90 healthy adolescents and young adults were selected with their consent, after selection they were categorized as non-obese and obese on the basis of their BMI. Results: The result showed that obese subjects had significantly low levels of 25(OH) vitamin D and higher levels of iPTH (P<0.001) when compared to non-obese subjects. It was found that only 26 subjects were vitamin D sufficient having vitamin D > 30 ng/ ml and they have normal BMI level (22.32 kg/m2). 56 subjects showed vitamin D insufficiency as they have vitamin D concentration 10-30 ng/ml and these subjects categorized as overweight or pre-obese according to their mean BMI level (28.63 kg/ m2), while 8 subjects showed vitamin D deficiency because they have vitamin D < 10 ng/ml and they were severely obese subjects with BMI 37.48 kg/m2. Conclusion: In our study 62% of our subjects consisted on adolescents and young adults showed insufficient status of vitamin D while 9% were showed deficient status with higher levels of iPTH and most of these have high BMI.