Background:No questionnaire is currently available for use in patients with anterior cruciate ligament (ACL) injuries in an Indonesian population. The most-used questionnaire in clinical research for these patients is the International Knee Documentation Committee (IKDC) Subjective Knee Form, as its psychometric properties are considered to be excellent.Purpose:To translate the IKDC into Indonesian and assess its validity for use in Indonesian-speaking patients with ACL injuries.Study Design:Cohort study (diagnosis); Level of evidence, 2.Methods:After a forward-and-backward translation procedure and cross-cultural adaptation, the validity and reliability of the questionnaire were investigated. The responses of ACL injury patients on 3 questionnaires, the Indonesian-IKDC (I-IKDC), 36-Item Short Form Health Survey, and Kujala Anterior Knee Pain Scale, were compared. Following consensus-based standards for the selection of health measurement instruments guidelines, construct validity, test-retest reliability, internal consistency, floor and ceiling effects, and measurement error were determined. The Bland-Altman method was used to explore absolute agreement.Results:Of 253 ACL injury patients, 106 (42%) responded to the invitation. Construct validity was considered good, as all predefined hypotheses on correlations between the I-IKDC and other scores were confirmed. Reliability proved excellent, with a high test-retest correlation (intraclass correlation coefficient = 0.99). Bland-Altman analyses showed no systematic bias between test and retest. Internal consistency was good (Cronbach α = .90). There were no floor or ceiling effects. Standard error of measurement was 2.1, and the minimal detectable change was 5.8 at the individual level and 0.7 at the group level.Conclusion:The I-IKDC, as developed, appeared to be a good evaluation instrument for Indonesian patients with ACL injuries.