Background: There have been several reports showing 20% to 40% failure after nonoperative functional treatment for acute lateral ligament disruption of the ankle. Hypothesis: Functional treatment after primary surgical repair has the advantage of decreasing the failure rate in comparison with functional treatment alone. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 132 feet of 132 patients were included in this study. Of these, 78 patients were treated with functional treatment alone (group F), and the remaining 54 patients were treated with functional treatment after primary surgical repair (group RF). The clinical results were evaluated using the Japanese Society for Surgery of the Foot Ankle-Hindfoot scale (JSSF) score, measuring the talar tilt angle and the anterior displacement of the talus in stress radiography, and noting the elapsed time between the injury and the return to the full athletic activity with no external supports. Results: The mean JSSF scores at 2 years after injury were 95.6 ± 5.0 points in group F and 97.5 ± 2.6 points in group RF ( P = .0669). The differences of the talar tilt angles compared with the contralateral side and displacement of the talus on stress radiography at 2 years after injury were 1.1° ± 1.5° and 3.6 ± 1.6 mm in group F, and 0.8° ± 0.9° and 3.2 ± 0.8 mm in group RF, respectively ( P = .4093, .1883). In group F, 8 cases showed fair to poor results, with JSSF scores below 80 points and instability at 2 years after injury. In group RF, 9 cases (9.4%) showed dorsum foot pain along the superficial peroneal nerve, which disappeared within a month. The time elapsed between the injury and the patient’s return to full athletic activity without any external supports was 16.0 ± 5.6 weeks in group F and 10.1 ± 1.8 weeks in group RF ( P < .0001). Conclusion: Nonoperative functional treatment alone and functional treatment after primary surgical repair showed similar overall results after acute lateral ankle sprain, but functional treatment alone had an approximately 10% failure rate and a slower return to full athletic activity. The authors recommend that treatment be tailored to suit each individual athlete.