Vitamin D resistant rickets (VDRR) is that type of rickets, which is resistant to the therapeutic doses of vitamin D that usually cure vitamin D deficiency rickets. (VDRR) may be acquired or genetic in origin. Four basic pathologic mechanisms are responsible for this disease. It includes :loss of phosphate in urine due to failure of reabsorpative mechanisms, failure of production of 1,25 dihydroxyvitamin D [1,25(OH)2D] ,end organ resistance to action of 1,25(OH)2D and lastly, renal tubular acidosis.The study was conducted on 25 patients and 10 healthy control, 21 patients was diagnosed as hypophosphatemic rickets and 4 patients hypocalcemic rickets. The patients group were (11 males & 14 females). All 25 patients had significant growth retardation and rachitic skeletal deformities, 16/25 had radiologic findings of active rickets and 9/25 had healing rickets. All patients had normal serum creatinine, blood urea nitrogen and elevated alkaline phosphatase activity. The hypophosphatemic group had significantly reduced serum phosphorus level and elevated 24 hour urinary phosphorus as well as low normal serum calcium. Elevated parathyroid hormone (PTH) was found in 11/21 patients. Serum 1,25(OH)2D was low in 17/21 patients and normal in 4/21. All hypocalcemic group had significantly low serum calcium and reduced urinary 24 hour calcium excretion as well as low normal serum phosphorus. PTH level was high in 3/4 patients, serum level of 1,25(OH)2D was low in 2 patients and normal in the other 2 patients. Significant positive correlation was found between serum phosphorus level and serum level of 1,25(OH)2D.