Background: The anterior cruciate ligament (ACL) is a principal stabilizer of the knee. ACL injuries are common in athletes and active young adults and generally require reconstructive surgery to achieve function and stability. As the methods of reconstruction are improved, objective biomechanical tests remain necessary to quantify knee stability once surgery is accomplished. Methods: In this prospective study, 60 patients (18–45 years) who underwent arthroscopic single-bundle ACL reconstruction were evaluated. Preoperative and 3, 6, and 12 months postoperative biomechanical evaluations were done. Standardized protocols included instrumented ligament laxity, motion analysis with 3D kinematic systems, and isokinetic quadriceps and hamstring muscle strength testing. Functional results were evaluated using the Lysholm Knee Score and International Knee Documentation Committee (IKDC) questionnaire. Results: Significant improvement in knee stability was observed at 3 to 12 months (p < 0.001). Instrumented examination revealed decrease in anterior tibial translation from 4 mm mean at 3 months to 2 mm at 12 months. Strength ratios of quadriceps and hamstrings were nearly-symmetrical at 12 months. Lysholm and IKDC scores were congruent with one another, and the majority of the patients (82%) achieved pre-injury or near pre-injury levels of activities at one year. Conclusion: ACL reconstruction led to considerable recovery of knee stability at 12 months. Repeated biomechanical evaluation provided objective confirmation of ligament function, muscle function, and functional capacity. These findings highlight the importance of including precise biomechanical evaluation in the rehabilitation process to optimize patient outcome.