BACKGROUND: The proportion of patients perceiving their symptoms as either acceptable or as a failure of treatment after anterior cruciate ligament reconstruction (ACLR) is unknown. Commonly used outcome scores such as the Knee injury and Osteoarthritis Outcome Score (KOOS) suffer from poor interpretability, and little is known about which scores represent an acceptable or failed postoperative outcome. PURPOSE: To determine the proportion of patients reporting acceptable symptoms or treatment failure at 6 to 24 months after ACLR and to define KOOS values corresponding to the patients' perceptions of treatment outcome. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: In 2012, a total of 1197 patients were randomly extracted from the Norwegian Knee Ligament Registry at 3 postoperative time points: 397 at 6 months, 400 at 12 months, and 400 at 24 months. The inclusion criterion was unilateral primary ACLR. Questions about acceptable symptoms and treatment failure and the KOOS questionnaire were sent to the patients, and those who answered "yes" to the acceptable symptoms question were considered to have acceptable symptoms. Patients who answered "no" to the same question and "yes" to the treatment failure question were considered to have treatment failure. Mean KOOS values and 95% CIs were calculated for each category. RESULTS: A complete data set was obtained from 598 (50%) responders. Fifty-five percent of the patients perceived their symptoms as acceptable at 6-month follow-up versus 66% at 12- to 24-month follow-up. Similarly, 7% at 6-month follow-up perceived their treatment to have failed versus 12% at 12- to 24-month follow-up. Postoperative mean KOOS subscale values ranged from 72 (95% CI, 70-74) to 95 (95% CI, 94-96) for patients with acceptable symptoms and from 28 (95% CI, 22-34) to 71 (95% CI, 65-76) for patients with treatment failure. For both categories, the worst subscale values were seen in the sport and recreation and quality of life subscales and the best in the activities of daily living subscale. CONCLUSION: Only half of the patients at 6 months and about two-thirds at 1 to 2 years perceived their symptoms as acceptable after ACLR. For these patients, KOOS values reflected no problems to mild problems on average, while for patients reporting treatment failure, KOOS values reflected moderate to severe problems.