Separated ossicles at the tip of the lateral malleolus, the condition known as os subfibulare, are sometimes a cause of ankle pain. There are two theories regarding the origin of os subfibulare. One theory proposes that it is caused by an avulsion fracture attributable to pull of the anterior talofibular ligament, whereas the other theory proposes that it is the result of an accessory ossification center. However, some authors have reported that os subfibulare is an avulsion fracture and few reports of accessory ossification have been described recently. A patient with os subfibulare that may have been caused by accessory ossification rather than an avulsion fracture was treated by the current authors.