A periacetabular osteotomy (PAO) is often sufficient to treat the symptoms and improve quality of life for symptomatic hip dysplasia. However, acetabular cartilage and labral pathologies are very commonly present, and there is a lack of evidence examining the benefits of adjunct arthroscopy to treat these. The goal of this study was to compare the clinical outcome of patients undergoing PAO with and without arthroscopy, with the primary endpoint being the International Hip Outcome Tool-33 (iHOT-33) at one year. In a multi-center study, two hundred and three patients who had symptomatic hip dysplasia were randomized: 97 patients undergoing an isolated PAO (mean age 27 years (range, 16 to 44); mean Body Mass Index (BMI) of 25.1 (range, 18.3 to 37.2); 86% women) and 91 patients undergoing PAO who had an arthroscopy [mean age 27 years (range, 16 to 49); mean BMI of 25.1 (17.5 to 25.1); 90% women]. At a mean follow up of 2.3 years (range, 1 to 5), all patients exhibited significant improvements in their functional score, with no significant differences between PAO plus arthroscopy versus PAO alone at 12 months post-surgery on all scores: pre-operative iHot-33 score of 31.2 (SD [standard deviation] 16.0) versus 36.4 (SD 15.9), and 12 months post-operative score of 72.4 (SD 23.4) versus 73.7 (SD 22.6)]. The pre-operative Hip disability and Osteoarthritis Outcome (HOOS)-pain score was 60.3 (SD 19.6) versus 66.1 (SD 20.0)] and 12 months post-operative [88.2 (SD 15.8) versus 88.4 (SD 18.3)]. The mean pre-operative physical health Patient-Reported Outcomes Measurement Information System (PROMIS) score was 42.5 (SD 8.0) versus 44.2 (SD 8.8) and 12 months post-operative [48.7 (SD 8.5) versus 52.0 (SD 10.6)]. There were four patients with PAO without arthroscopy who required an arthroscopy later to resolve persistent symptoms, and one patient from the PAO plus arthroscopy group required an additional arthroscopy. This Randomized Controlled Trial (RCT) has failed to show any significant clinical benefit in performing hip arthroscopy at the time of the PAO at one-year follow-up. Longer follow-up will be required to determine if hip arthroscopy provides added value to a PAO for symptomatic hip dysplasia.