BACKGROUND: Wearable activity-measurement devices are increasingly popular among the public, but there is little information regarding their use among patients undergoing sports medicine procedures. The purpose of this study was to compare accelerometer-measured data with traditional patient-reported measures and to determine the trajectory of physical activity from before surgery to 1 year after anterior cruciate ligament reconstruction. MATERIALS AND METHODS: Adult patients undergoing primary anterior cruciate ligament reconstruction were enrolled in this prospective cohort pilot study. The Tegner activity scale, Marx activity scale, International Physical Activity Questionnaire Short Form (IPAQ-SF), Knee injury and Osteoarthritis Outcome Score (KOOS), and EuroQoL-5D were administered preoperatively and 3, 6, and 12 months postoperatively. At these intervals, each patient was asked to wear an accelerometer for 7 consecutive days. Time spent in moderate-to-vigorous physical activity (MVPA min/wk), metabolic equivalents of physical activity, and average daily steps were calculated from the accelerometer output and correlated with patient-reported measures. RESULTS: Twenty-eight patients were included in this study. Of the 28 patients, 20 remained, and at the 12-month analysis, 18 patients were analyzed. There were significant improvements in Tegner activity scale score, KOOS symptoms, sports/recreation, and quality of life subscales, and IPAQSF MVPA min/wk at final follow-up. All accelerometer-based outcomes had improvements at 3, 6, and 12 months. CONCLUSION: The accelerometer may be a useful tool for understanding patients' activity levels at different time points during their recovery and for providing tangible targets for patients to achieve at least an average recovery. [