Both os trigonum syndrome and osteochondral lesion of talus (OLT) are common causes of ankle pain and usually affect ballet dancers or athletes. Lateral osteochondral lesions, which usually result from traumatic event, are mostly located anterolateral talar dome but rare central or posterolateral. Moreover, there are technical difficulties such as position of patient or additional posterior portal to address posterolateral lesion by arthroscopy. Meanwhile, treatment of os trigonum syndrome using arthroscopic approach has been reported in many literatures recently. However, it has not been reported to diagnose both os trigonum syndrome and posterolateral OLT together and treat arthroscopically at one stage. The authors report a case of male patient who was diagnosed as os trigonum syndrome with posterolateral OLT and treated simultaneously by hindfoot arthroscopy. Symptom was improved immediately after the operation, and radiological findings at postoperative 16 months verified remarkable healing.