Purpose <p>All-inside arthroscopic repair of the anterior talofibular ligament (ATFL) using two or three portals is one of the most commonly performed procedures for managing chronic lateral ankle instability (CLAI). However, it remains unclear whether there are differences in functional outcomes between the use of two versus three portals.</p> Methods <p>This retrospective comparative study included 66 patients with CLAI who underwent an all-inside arthroscopic isolated ATFL repair procedure between 2018 and 2021. Patients were divided into two groups according to the number of portals introduced. In the two-portal group (n = 31), the ATFL was repaired using two portals. In the three-portal group (n = 35), the ATFL was repaired using three portals. The American Orthopedic Foot and Ankle Society (AOFAS) scores, Karlsson Ankle Function Score (KAFS), Anterior Talar Translation (ATT), Active Joint Position Sense (AJPS), complications, as well as the time of return to sports were compared between the two groups.</p> Results <p>All patients were followed up for a minimum of 2&#xa0;years. Improvement in functional outcomes (AOFAS, KAFS, ATT and AJPS) was recorded at the final follow-up. No significant differences were observed between the two groups in terms of operative time, AOFAS, KAFS, ATT, AJPS, or the time of return to sports. However, no nerve complications were observed in the two-portal group.</p> Conclusion <p>In patients with CLAI undergoing all-inside arthroscopic isolate ATFL repair, the use of either two or three portals results in comparable and favorable functional outcomes. The two-portal procedure was also associated with no superficial peroneal nerve injuries.</p> Level of evidence <p>Level III.</p>