This study assessed the use of semirigid hip orthosis to stabilize the femoral head into the acetabulum in the delayed treatment of developmental dysplasia of the hip (DDH; Graf type IIb or more severe) under the age of 6 months. Ninety-eight hips from 75 patients (four boys, 71 girls) were evaluated retrospectively. The mean age at treatment initiation was 3.2±1.3 months (1–6 months). As the dysplastic hip matured into a type I hip, we applied the weaning regimen for 1 month. Seventy-two patients (96%) were treated successfully in 4.2±1.1 months (2–8 months). All of the failures were type IV hips. We did not detect any acetabular or femoral head pathology in the later follow-up. Semirigid hip orthosis is safe and effective as the first-line treatment method for delayed DDH except in type IV hips in patients under 6 months of age.Level of Evidence: Level IV. Case series.