The KT-1000 knee arthrometer (KT-1000) is an objective instrument to measure anterior tibial motion relative to the femur for anterior cruciate ligament (ACL) reconstruction. Four studies between 1950 and 2007 regarding validity of the KT-1000 were identified using a Medline search. One had interpretable information on sensitivities, specificities, and predictive values to validate the instrument as a diagnostic tool in patients with acute or chronic ACL injuries. Three had limitations in methodology. We suggest that the KT-1000 should be used with caution as an objective instrument. Rather, using a KT-1000 score derived by subtracting the anterior tibial motion relative to the femur of the injured knee to that of the uninjured knee may be more appropriate as a dichotomous diagnostic test with a threshold of 2 or 3 mm.