Giant cell tumor of bone (GCT) is a benign neoplasm that most commonly presents with pain and is rarely diagnosed as an incidental finding. We present the report of a young woman whose pre-operative MRI was only noted to have a tear of the anterior cruciate ligament (ACL). Subsequently, the patient underwent anACL reconstruction. A second MRI, performed four years later, demonstrated an enlarged mass in the same location. A retrospective evaluation of the initial MRI revealed an eccentric metaphyseal lesion. Histology obtained from the lesion demonstrated a giant cell tumor of bone. We present the case of an asymptomatic GCT discovered retrospectively as an incidental finding and reevaluated four years later. 'Ihis case serves as a reminder of the importance for the critical review of routine preoperative imaging and also offers a unique perspective on the natural history of giant cell tumor of bone.