Background: During inversion injuries of the ankle joint, the anterior talofibular ligament (ATFL) is the most commonly injured structure. Injuries to the lateral collateral ligaments of the ankle, either in isolation or in combination with injury to the calcaneofibular ligament (CFL), account for approximately 60-65% of all ankle ligament injuries. In recent years, several studies have examined the impact of lateral ankle ligament injuries on lifestyle and overall health. Repeated inver sion injuries-particularly those occurring three or more times-can lead to chronic ankle instability (CAI). In the treatment of ankle instability, both open and arthroscopic surgical techniques are widely used internationally. In Mongolia, there is an increasing clinical need to evaluate and compare the outcomes of arthroscopic versus open surgical repair of lateral ankle ligament injuries. This need forms the basis of the current study. Aim: The comparative studies on open vs arthroscopic anterior talofibular ligament (ATFL) repair are limited. This study aimed to compare the early therapeutic efficacy and cost between the traditional open Broström-Gould repair and all-ar throscopic anatomical repair of the ATFL for chronic lateral ankle instability. Materials and Methods: A total of 40 patients with chronic lateral ankle instability undergoing repair of the ATFL be tween September 2024 and February 2025 were retrospectively included with a traditional open surgery (n=10) group and an arthroscopy (n=17) group. The surgery duration, surgical cost, postoperative complications, and the preoperative/ postoperative American Orthopaedic Foot & Ankle Society Score (AOFAS) and Karlsson-Peterson score were compared between groups. Results: Compared to the anatomical group, the non-anatomical group had significantly shorter surgery and hospitaliza tion durations. Three months after the operation, the AOFAS and Karlsson scores significantly improved in both groups. Nevertheless, there was no significant difference in the AOFAS and Karlsson scores between groups at both preoperative and postoperative assessments. No significant difference was found in the incidence of postoperative complications be tween the two groups. Conclusion 1. These results suggest that open Broström-Gould repair and all-arthroscopic anatomical repair of the ATFL have comparable therapeutic efficacy for chronic lateral ankle instability. 2. The arthroscopic surgery had a smaller incision, while the open Broström-Gould had a shorter surgery duration and lower cost.