Purpose The purpose of our study is to evaluate the clinical results of anatomical reconstruction of the lateral ligaments with semitendinosus allograft. Methods Thirty-six patients with chronic lateral instability underwent anatomical reconstruction of the lateral ligaments of the ankle with semitendinosus allograft. The American Orthopaedic Foot and Ankle Society Ankle-Hindfoot Scale score (AOFAS score) and the Karlsson score were used to evaluate the clinical results before and after surgery. Results A total of 35 patients (97.2 %) (36 ankles) were followed up for a mean of 37.9 months. The mean AOFAS score improved from 42.3±4.9 points preoperatively to 90.4± 6.7 postoperatively. The mean Karlsson score improved from 38.5±3.2 preoperatively to 90.1±7.8 postoperatively.Conclusions Anatomical reconstruction of the lateral ligaments with semitendinosus allograft achieves a satisfactory surgical outcome for chronic ankle instability.Ankle sprains are reported to be the most common sports injury and account for 10∼15 % of sports-related injuries [1][2][3]. Although the majority of the patients have successful results after conservative treatment, up to 20-40 % have mechanical instability requiring operative intervention [4,5].There are various operative procedures to treat chronic lateral ankle instability. If the patient has a weak remnant of the lateral ligament, generalised joint laxity or previous failed operation for lateral ankle instability, anatomical lateral ligament reconstruction is always suggested [6].Several kinds of graft are used for the anatomical ligament reconstruction. Compared to the autograft, an allograft has the advantages of no donor site morbidity, shorter operation time and less postoperative pain [7]. Furthermore, with the improvement of the sterilisation technique, some potential complications, for example, the potential for disease transmission, osteolytic reactions, etc., have been markedly decreased [7,8]. Up to now, there have been few reports about the use of allograft for lateral ankle ligament reconstruction. We use a semitendinosus allograft in lateral ankle ligament reconstruction and propose that anatomical reconstruction of the lateral ligaments with this allograft can achieve a satisfactory surgical outcome for chronic ankle instability.