Background: This study aimed to adapt the Knee injury and Osteoarthritis Outcome Score- Anterior Cruciate Ligament (KOOS-ACL) into Turkish and to assess its validity and reliability. Methods: The adaptation process involved translation, back-translation, and cultural adaptation of the questionnaire. Totally 133 patients who had a diagnosis of anterior cruciate ligament tear was recruited. The reliability of the Turkish version of the KOOS-ACL was assessed using Cronbach’s alpha, item-total correlations, and ICC. EFA and CFA were performed to evaluate construct validity, supported by KMO and Bartlett’s test results. Criterion validity was examined through correlations with IKDC scores, and discriminative power was assessed using an independent samples t-test. Results: IKDC score for evaluating knee function was 59.84 ± 21.74. The composite KOOS-ACL-Tr score was 61.95 ± 25.19. Cronbach’s Alpha value was found to be 0.952 demonstrating high reliability. KOOS-ACL-Tr scores showed a linear positive correlation with the time elapsed since injury and IKDC scores (p < 0.001) establishing concurrent validity. Conclusions: The adapted Turkish version of the KOOS-ACL is a valid and reliable scale intended for use in monitoring patients with ACL injuries.