Deficiency of vitamin D is an emerging issue in children worldwide. It has been observed that all patients with vitamin D deficiency does not manifest clinical features or hyperparathyroid response. In this study we have evaluated the interaction of serum vitamin D level, parathyroid hormone (PTH) level and bone mineral density (BMD) in children. Objectives: Our objectives were to determine the frequency of Vitamin D deficiency in children and association of low serum D level with serum parathyroid level and bone mineral density (BMD). Study Design: Descriptive cross sectional study. Period: June 2012 to May 2014. Setting: Pediatric and Orthopediatric out-patient departments. Material & Methods: A total of 500 children up to 15 years with low serum vitamin D level were enrolled to analyze the interaction of Serum vitamin D, PTH and BMD. Patients were divided in groups on the basis of serum PTH. We have categorize the deficiency of Vitamin D on the basis of level of 25OHD. It was defined as severe (25OHD ≤ 5 ng/ml), moderate (25OHD≤ 10 ng/ml) and mild (25OHD ≤ 20 ng/ml) and hyperparathyroidism (SHPT) was valued if level >65 pg/ml. All children with 25OH ≤ 20 ng/ml were included and association with SHPT and BMD were measured. Results: It has been observed that 30–40% of patients with moderate and severe deficiency of vitamin D respectively had shown increased level of PTH. Bone mineral density has demonstrated decline pattern from PTH Quartile 1to Quartile 4 at all sites in children, with only minimal difference (decreasing trend) in serum 25OHD levels between these quartiles. The critical level of parathyroid hormone beyond which BMD going to decline is 35 pg/ml. No demonstrable difference has been observed in BMD within each PTH quartile according to categorization of Vitamin D Deficiency. Conclusions: Around 40% of the patients having low serum vitamin D level demonstrated SHPT. Regarding the BMD levels, it begins to decreases at PTH levels currently well thought-out to be normal. So there is a need to re-define SHPT among different age groups considering the relationship linking PTH and BMD. This may also affect guidelines regarding vitamin d supplementation in patients with vitamin D deficiency.