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.