Abstract: Developmental Dysplasia of the Hip (DDH) is a common congenital malformation. Avascular necrosis of femoral head is the major complication of both close and open reduction of the dislocated joint. Aim of this study was to determine the incidence and influencing factors in different types of a vascular necrosis of femoral head, following surgical treatment of developmental dysplasia of hip in 1-7 years patients. In this study, 120 patients aged from 1 to 7 years old with DDH who had been undergone open surgery, entered to the study. All of these patients followed up for at least 1 year. Surgery procedures divided to 4 groups: open reduction, open reduction+salter osteotomy, open reduction+femur shortening and open reduction+salter osteotomy+femur shortening. The presence of Avascular Necrosis (AVN) had been appraised. 27.5% of surgeries performed on male and 72.5 on female patients. 35.0% of DDH cases were unilateral and remaining was bilateral. 36 patients (30%) shows radiologic findings of AVN, although all of them placed at group I of Bucholz-Ogden classification. 40% of group A patients, 25% of group B, 14.3% of group C and 36.4% of group D patients developed this findings. Open reduction of DDH in older children is effective in the management of DDH and if all of the contrivance considered in the surgery, the rate of AVN would be low and mild (at least in short term follow ups).