Objective: To compare the clinical outcomes of horizontal mattress suture vs free-edge suture in the all-inside arthroscopic Broström-Gould procedure. Methods: This retrospective cohort study included 68 chronic lateral ankle instability (CLAI) patients who underwent either a horizontal mattress suture or a free-edge suture all-inside arthroscopic Broström-Gould procedure from January 2014 to January 2017. Patients were divided into two groups based on the suture fashion during the all-inside arthroscopic Broström-Gould procedure. In the horizontal mattress suture group (n = 31), anchor sutures were used to suture the ATFL, capsule, and inferior extensor retinaculum in horizontal mattress suture fashion. In the free-edge suture group (n = 37), anchor sutures were used to suture the ATFL, capsule, and inferior extensor retinaculum in free-edge suture fashion. The Visual Analogue Scale (VAS) score, the American Orthopaedic Foot and Ankle Society (AOFAS) score, Karlsson Ankle Functional Score (KAFS), Anterior Talar Translation (ATT), the rate of return to sports, and ankle proprioceptive recovery were compared in both groups. Results: The operative times and duration of hospitalization between the two groups were comparable (all P > 0.05). The VAS, AOFAS, ATT, the rate of return to sports, and ankle proprioceptive recovery were comparable between the horizontal mattress suture and free-edge suture groups at 1 and 2 years after surgery. Patients of the free-edge suture group achieved better KAFS 1 and 2 years after the surgery compared with those of the horizontal mattress suture group. In both groups, incisions were healed by first intention, and complications such as infection, implant reactions, tendon injury, and nervous or vascular injuries were not observed. The ankle proprioceptive recovery in horizontal mattress suture and free-edge suture groups showed no significant differences at 1 and 2 years after surgery. The mean time of the return to full activity for patients in the horizontal mattress suture group was 10.38 AE 2.02 (range 8 to 12) weeks vs 8.63 AE 2.31 (range 8 to 12) weeks for those in the free-edge suture group (P = 0.001, power = 0.907). The exercise participation rates were comparable between groups (P > 0.05). At the 2-year follow-up, all patients regained normal activities and ankle stability, and no recurrence of CLAI or revision surgery was recorded. Conclusion: All-inside arthroscopic Broström-Gould surgery for the treatment of CLAI ensures a better functional effect (KAFS) and better recovery time when free-edge suture is used instead of horizontal mattress suture.