There has been a renewed interest in the anterolateral structures of the knee, including description of the anterolateral ligament (ALL) as a distinct structure. Recognizing injury to the ALL is challenging, particularly given the subjective nature of physical examination. Consequently, focus has turned to magnetic resonance imaging (MRI) to reach a preoperative diagnosis of this region. The aim of this study was to examine the ability of 3-Tesla (3T) MRI to identify the ALL in ACL-injured patients compared to a matched control group of ACL-intact patients. The hypothesis was that the ALL would be more difficult to identify in ACL-injured patients compared to ACL-intact patients.A prospective case control study was performed comparing 3T MRI scans of 63-patients with an ACL rupture with a control group of 64-patients without ACL injury. An experienced musculoskeletal radiologist and an orthopaedic surgeon evaluated the scans performed using standard knee protocols. The ALL was considered in three regions for analysis: femoral, meniscal, and tibial. The status of the ALL was determined as visualized or non-visualized, and the integrity was assessed as intact, attenuated, or focal discontinuity.The detection rate of at least a portion of the ALL was 41/64 (64%) in the control group and 45/63 (72%) in the ACL-injured cohort, respectively. The entire length of the ALL could only be identified in 15/64 (23%) of the control group and 13/63 (21%) of the ACL-injured cases. In both groups, the visibility of the ALL was poorest at the femoral region and greatest at the tibial regions. The ALL, when visualized, was deemed to be intact in 55/63 (87%) of cases. Although the inter-observer reliability was excellent for detection of the ALL in the control group (κ = 0.86), this decreased to only moderate reliability in the ACL-injured group (κ = 0.52).This study demonstrates that MRI alone should not be relied upon to make a diagnosis of ALL injury in the setting of concomitant ACL injury due to the inability to accurately visualize this structure consistently in its entirety. To make a diagnosis of ALL injury or anterolateral instability of the knee and clinical correlation remains essential.Case-control study, Level III.