We examined 188 consecutive patients, each of whom had an acute ankle sprain, using clinical stability assessment, stress radiographs, and arthrography to compare the reliability of these methods used in diagnosing lateral ligament ruptures of the ankle. Sixty-six of the ankles were treated operatively. Arthrography accurately detected ligament damage in all of the patients with this injury and revealed the extent of the injury in about 85%, whereas clinical examination and stress radiographs detected only about half of the injuries. The injuries and the results of these two methods were often controversial, as our study will show.