We evaluated long-term follow-up clinically and radiologically of patients with developmental dysplasia of the hip operated between 1956 and 1971 with adductor tenotomy and open reduction of the hip. Ninety-six patients with developmental dysplasia of the hip were operated between 1956 and 1971. Their ages were from 10 months to 44 months. Eighty-eight patients (88.5%) were girls and 11(11.5%) were boys. There were 58 unilateral cases and 38 bilateral cases for a total of 134 operated hips. The cases with bilateral involvement were operated simultaneously. For all patients, the surgical team used the same technique consisting of open reduction through a Smith Petersen incision together with an adductor tenotomy and lengthening or tenotomy of the Psoas muscle. Postoperative immobilization was a pelvic-toe cast for one month followed by two plaster casts with abduction rod for three to five months. Postoperative follow-up was from 15 years to 44 years, 4 months (mean: 24 years, 4 months). The clinical outcome evaluated pain, range of motion, limp, muscle strength, and leg length discrepancy. Radiological evaluation included Mose index, acetabular head index, Wiberg’s CE angle, medial articular space, Sharp’s angle, acetabular index of the weight-bearing zone, acetabular depth, radial quotient in unilateral cases, width and shape of teardrop, collodiaphyseal angle, Shenton line, and degenerative changes of the hip. The results of clinical evaluation were: Excellent – 60 (44.7%), Good – 35 (26.1%), Fair – 26 (19.4%), Poor – 13 (9.7%). Radiological results according to a modified Severin classification were: Class I – 60 (44.7%), Class II – 33 (24.6%), Class III – 31 (23.1%), Class IV – 9 (6.7%), Class V – 1 (0.7%), Class VI – 0 (0%). Complications were: infections in six hips (4.4%), three (2.2%) being deep ones. Avascular necrosis according to Bucholz and Odgen occurred in 38 hips (28.3%). Four hips (3%) were Type I, 31 hips (23.1%) were Type II, three hips (2.2%) were Type III. Degenerative changes occurred in 29 hips (21.6%) of which seven hips (5.22%) were Grade I, 12 hips (8.95%) were Grade II, and 10 hips (7.46%) were Grade III. Our conclusions were: 1.) Open reduction of developmental dysplasia of the hip is a valid method in late treatment or failure of orthopaedic treatment. 2.) Clinical results are better than radiological results. 3.) The rate of degeneratives changes increases with long-term follow-up. 4.) The best radiological results are achieved in patients who are younger than one and half year of age at the time of surgery. 5.) There was a significant rate (23.1%) of avascular necrosis Type II according to the Bucholz and Odgen classification, but this can only be realized with long-term follow-up.