Dega acetabuloplasty at the time of open reduction is effective in improving the acetabular coverage of the femoral head, hence improving the stability of reduction and preventing possible surgery in the future for residual acetabular dysplasia in older children with Tönnis grade 3 and 4 developmental dysplasia of the hip (DDH). The aim of this study was to assess the radiological results of open reduction combined with Dega osteotomy in DDH. Twenty-two children’s 26 hips were operated on at a mean age of 38±20.4 SD months and followed up for an average of 42 (range 24–108) months. Thirteen hips (50%) were operated on with concomitant open reduction and capsulorrhaphy, and 13 hips (50%) were treated with concomitant open reduction, capsulorrhaphy and femoral shortening osteotomy. Radiological examination included acetabular index (AI) and centre edge angle measurements. The mean preoperative AI was 39.4±6.9° SD, which improved to 18.3±4.5° SD postoperatively, and AI was measured as 15±3.5° SD at the latest follow-up. There was a significant difference in the mean AI values between the last follow-up and the preoperative measurements (P<0.05). The mean centre edge angle was 31±5.6° SD postoperatively, and it was 31±6.2° SD at follow-up. There was no significant difference between the two values. Two hips were noted to have lateralization of the femoral head due to coxa valga anteverta. One of them was operated with a femoral varus osteotomy. The Dega osteotomy combined with anterior open reduction and femoral osteotomies is a safe and effective acetabular osteotomy for surgical treatment of severe DDH such as Tönnis grade 3 and 4 dislocations.