We present a longitudinal observational study on classification of acute lateral ankle ligament injuries in track and field athletes, based on objective criteria. These very common and sometimes troublesome sports injuries are treated functionally, but there is a lack in international literature on predicting the time needed for full recovery. Taking into consideration (1) active range of motion, (2) edema, (3) stress radiographs findings, and (4) full rehabilitation time, we divided grade III sprains in IIIA and IIIB, proposing that these injuries can be classified in four categories (I, II, IIA, IIIB). The range of motion-edema-stress radiographs classification that we propose evaluates the severity of lateral ankle injuries, is an easy and practical method, and predicts full return in athletic activities without residual complaints, if the proper rehabilitation program is executed.