Many clinicians believe that the results of revision anterior cruciate ligament (ACL) reconstruction compare unfavorably with primary ACL reconstruction. However, few prospective studies have evaluated revision ACL reconstruction using validated patient-based metrics. This study was performed to evaluate and compare the results of revision ACL reconstruction and primary ACL reconstruction. The Multicenter Ortho- paedic Outcomes Network consortium is an NIH-funded, hypothesis-driven, multicenter prospective cohort study of patients undergoing ACL reconstruction. All patients pre- operatively complete a series of validated patient-oriented questionnaires. At scheduled 2- year follow-up all patients are given the same series of questionnaires to complete. The study evaluated the results of 2-year follow-up of revision ACL reconstruction performed in 2001. Parameters evaluated included Marx activity level, Knee Injury and Osteoarthritis Outcome Score (KOOS), and International Knee Documentation Committee (IKDC) scores. For this study 446 subjects met inclusion criteria; 2-year follow-up was obtained on 393 (88%). The study group consisted of 55% males with median age of 22 years. There were 33 revision ACL reconstruction cases, for which follow-up was available for 29 (88%). Median baseline Marx (interquartile range) was 12 (8 to 16) and 12 (6 to 16) for the primary ACL reconstruction and revision ACL reconstruction groups, respectively (p1⁄40.81). At 2 years, median Marx was 9 (4 to 13) and 5 (0 to 10) for the primary ACL reconstruction and revision ACL reconstruction groups, respectively (p1⁄40.03). Median 2-year IKDC was 75.9 (revision) versus 83.9 (primary) (p1⁄40.003). Median KOOS subscale Knee Related Quality of Life (KRQOL) at 2 years was 62.5 (revision) versus 75 (primary) (p < 0.001), subscale Sports and Recreation was 75 (revision) and 85 (primary) (p 1⁄4 0.005), subscale Pain was 83.3 (revision) and 91.7 (primary) (p 1⁄4 0.002). Marx activity score declined at 2-year follow-up in revision ACL reconstruction compared with primary ACL reconstruction. IKDC and KRQOL were significantly decreased in revision ACL reconstruction compared with primary ACL reconstruction at 2-year follow- up. Revision ACL reconstruction resulted in a significantly worse outcome as measured by these patient-based measures at 2 years.