Avascular necorosis of femoral head following treatment of congenital disloction of the hip(CDH) is one of serious complications that may come from iatrogenic causes. The reported incidences and pathogenesis of necrosis suggested have varied greatly among authors. In spite of the various efforts to decrease the complication, the recently reported incidences remain still in plateau. We reviewed eighty three children treated for CDH's at Korea University Guro Hospital from Sept. 1983, to May, 1989 and studied the incidence of avascular necrosis and influence of associated factors regarding the radiological and clinical outcome of avascular necrosis. The following results were obtained; l. Of the eighty-three hips, sixteen (19.2% ) had some evidence of avascular necrosis (total avascular necrosis eleven hips, partial avascular necrosis five hips) according to Salter's Gage's criteria. 2. Incidence of avascular necrosis of femoral head was 8.3% (1/12) in children at the age less than six months, 14.3% (5/35) between six months to eighteen months, 41.2% (7/17) between eighteen months to thirty six months and 15.8% (3/19) in over three years at the beginning of treatment. 3. Four of forty-four hips(9.0%) treated with closed reduction developed avascular necrosis of femoral head. The avascular necrosis developed in twelve (30.7%) of surgically treated thirty-nine hips (six of eleven hips treated with open reduction only, four of eleven hips with Salter's osteotomy, two of four hips with open reduction and femoral shortening, none of thirteen hips with open reduction, femoral shortening and Salter's osteotomy). 4. Of the sixteen hips complicated with avascular necrosis nine hips belonged to good, three hips to fair, four hips to poor according to the Roentgenographic grading by Thomas (1989). 5. Functional assessments of the 16 hips of avascular necrosis was made according to Brougham's(1990) criteria and there were Excellent in 3 cases, Good in eight cases, Fair in three cases, Poor in two cases.