This case report describes a nine-year-old girl with bilateral Tönnis type 2 developmental dysplasia of the hip (DDH) that had not been treated previously. A notable feature of this patient was the presence of a simple cystic lesion in the left supraacetabular region. We performed a Pemberton osteotomy and used a hydroxyapatite (HA) wedge in the area of the supraacetabular cyst. Our aim was to evaluate the safety and efficacy of using an HA wedge in DDH cases with accompanying supraacetabular cysts. At the 13-month clinical follow-up, no complications were observed at the hip, including issues with wound healing, non-union, loss of graft position, or infection. Although the hip dislocation was not fully corrected by the final follow-up, no graft-related complications were encountered. In conclusion, based on our experience with this case, we believe that the use of an HA wedge can be both effective and safe in DDH patients with supraacetabular cysts. Additionally, HA wedge use is minimally invasive and may reduce donor site morbidity, as no additional incisions or osteotomies are needed to obtain the graft.