This is a case report of a 26-year-old healthy female who sustained an isolated posterior malleolar fracture; diagnosed by X-ray, confirmed by CT and treated with an orthosis and full weightbearing. Subsequent weightbearing X-rays showed no displacement or concomitant injury. However rare, isolated posterior malleolar fracture may indicate a complex ankle injury and therefore warrant extra attention when diagnosed. The diagnosis is difficult due to diffuse symptoms and limited visualization on plain X-rays. Missed diagnoses might lead to persistent pain and arthrosis.