BACKGROUND Osteoarthritis secondary to developmental dysplasia of the hip (DDH) is one of the major causes of hip pain and disability. The aim of the study was to compare the effectiveness of prolotherapy (PrT) injections versus exercise protocol for the treatment of DDH. MATERIAL AND METHODS There were 46 hips of 41 patients who had osteoarthritis secondary to DDH included in this study. Patients were divided into 2 groups: treated with PrT (PrT group; n=20) and exercise (control group; n=21). Clinical outcomes were evaluated with visual analog scale for pain (VAS) and Harris hip score (HHS) at baseline, 3 weeks, 3 months, 6 months, and a minimum of 1-year follow-up. In PrT group clinical results were also compared in Crowe type I-IV hips. RESULTS Between group analysis revealed no significant between group differences at baseline. Dextrose injection recipients out performed exercise controls for VAS pain change score at 6 months (-4.6±2.6 versus -2.8±2.5; P=0.016), and 12 months (-4.5±2.4 versus -2.9±2.5; P=0.017) and for HHS at 6 months (24.2±14.0 versus 14.8±12.4; P=0.007) and 12 months (24.3±13.4 versus 16.5±11.3; P=0.018). CONCLUSIONS To our best knowledge, this study is the first regarding the effects of an injection method in the treatment of osteoarthritis secondary to DDH. According to our study, PrT is superior to exercises. PrT could provide significant improvement for clinical outcomes in DDH and might delay surgery.