Sixty-five patients who consecutively underwent anterior cruciate ligament reconstruction were studied using four individual, categoric, knee score rating systems. Different results were noted at followup (mean, 35 months; range, 24 to 58) depending on the rating method used. Ali patients were graded using the Hospital for Special Surgery, Lysholm, Tegner activity, and Cincinnati Knee Ligament rating systems. The Cincinnati Knee Ligament rating individual scores were noted to be lower than the Hospital for Special Surgery and Lysholm scores for subjective and objective outcome assessment. The Hospital for Special Surgery and Lysholm scores did not correlate highly with the Cincinnati Knee Ligament rating final rating, but they did correlate with each other. The use of ligament rating scores tended to inflate results, particularly when raw scores were converted to overall categoric ratings (e.g., excellent, good). The Cincinnati Knee Ligament rating system correlates more highly with individual grading and most precisely defines outcome in athletically active patients. Sources of error may be introduced by a disproportionate combination of unrelated scores or by overrating low-activity-level individuals who avoid stressing their knees. Avoidance of data generalization remains the optimal method for studying anterior cruciate ligament surgery outcome.