This study examined the relationship between impairment of the knee and activity restriction during activities of daily living and sports following anterior cruciate ligament reconstruction. Knee range of motion, swelling, pain, instability, ligamentous laxity, isometric and isokinetic muscle function and performance-based measures of activity restriction were measured in 44 subjects. Four measures of patient-reported activity restrictions, including the Activities of Daily Living, Sports Activities Scales of the Knee Outcome Survey, and global ratings of function during activities of daily life and sports, were statistically combined to create a composite variable representing the level of patient-reported activity restrictions for each subject. Hierarchical regression analysis revealed that 17% of the variability in patient-reported activity restrictions was accounted for by age, length of postoperative follow-up, and mechanism of injury. Addition of the one-legged hop, Lachman, anterior drawer, and varus stress tests accounted for an additional 40% of the variability of function. When pain and giving way were added to the model, 79% of the variability was explained.