Introduction: Chronic lateral ankle instability occurs in up to 20% of ankle injuries. Most can be treated conservatively, but surgical reconstruction is required if conservative treatment fails. Modified Broström–Gould procedure is an effective surgical treatment and the augmentation of this procedure with a periosteal flap may confer additional stability. We report on the outcome of a technique combining a modified Broström–Gould procedure augmented with a periosteal flap in patients with chronic lateral ankle instability. Method: Twenty-four males aged 18–42 (mean, 24) with chronic lateral ankle instability affecting 24 ankles underwent the modified Broström–Gould procedure augmented with a periosteal flap, and these surgeries were performed by a single surgeon. The mean follow-up period was 28.7 months. Patients were assessed pre- and post-operatively with the American Orthopaedic Foot and Ankle Society (AOFAS) ankle and hind foot score. Results: Preoperatively, the mean AOFAS ankle and hind foot score was 67.38. Post-operatively, significant improvement was seen, with a score of 88.71 ( p < 0.05). None of the patients reported surgical or wound complications. Conclusion: The technique of modified Broström–Gould procedure with periosteal flap augmentation appears to be a simple and safe operation for chronic lateral ankle instability. Patients with poor quality local ligamentous tissue, obese patients or high demand athletes generally benefit from this procedure. It allows effective augmentation of the reconstruction without causing any harm to local tendons or using additional costly implants.