BACKGROUND: The arthroscopic management of borderline hip dysplasia (BHD) is controversial, and long-term follow-up data are scarce. The purpose of this study was to report prospectively collected survivorship and patient-reported outcome measures (PROMs) at a minimum 10-year follow-up following primary hip arthroscopy with capsular plication and labral preservation in patients with BHD. METHODS: Data were prospectively collected on all patients who underwent primary hip arthroscopy between September 2008 and September 2011. Patients with BHD (defined by a lateral center-edge angle [LCEA] between 18° and 25°) were included. Preoperative and minimum 10-year follow-up scores for the modified Harris hip score (mHHS), Nonarthritic Hip Score (NAHS), Hip Outcome Score-Sports Specific Subscale (HOS-SSS), and visual analog scale (VAS) for pain were collected. Exclusion criteria were prior ipsilateral hip surgery, Workers' Compensation status, Tönnis grade of >1, previous hip conditions, or LCEA of <18°. Survivorship was defined as no conversion to total hip arthroplasty (THA). The risk factors for THA conversion were analyzed. The achievement rate for the minimal clinically important difference (MCID) was reported. A propensity-matched comparison with a control group without BHD was performed. RESULTS: Forty-five (80%) of 56 eligible hips were included in this study: 38 hips (84%) of female patients and 7 hips (16%) of male patients. The mean patient age was 31.0 ± 12.9 years, and the mean patient body mass index (BMI) was 24.5 ± 5.4 kg/m 2 . The 10-year survivorship was 82.2%, and there was significant improvement in all PROMs and VAS pain from baseline to the minimum 10-year follow-up (p < 0.001). The odds of undergoing conversion to THA were 4.4 times higher for patients with a BMI of ≥23 kg/m 2 and 7.1 times higher for patients who were ≥42 years of age. The MCID was achieved at high rates for the mHHS (79%), NAHS (79%), HOS-SSS (70%), and VAS pain (76%). The minimum 10-year survivorship, PROMs, and MCID achievement rates for the BHD group were comparable with those for the control group. CONCLUSIONS: Patients with BHD who underwent primary hip arthroscopy with capsular plication and labral preservation demonstrated an overall survivorship of 82.2% and significant improvement in all PROMs and achieved the MCID at high rates at a minimum 10-year follow-up. LEVEL OF EVIDENCE: Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.