This study evaluated the accuracy of MRI in the diagnosis of mechanically produced partial anterior cruciate ligament (ACL) tears in hind limb specimens of sheep. An animal model to produce partial ACL tears was developed. Fifteen sheep were analyzed, with one knee from each sheep serving as a control. All 30 ACLs were excised and sent for histopathology. On gross inspection, all 15 knees had posterolateral portion (PLP) involvement, whereas only four had anteromedial portion (AMP) involvement. MRI interpretation also disclosed that all 15 knees had PLP disruption but revealed 10 knees to have AMP involvement. The six knees labeled intact on gross examination but disrupted by MRI standards were seen to have microscopic tears. This study shows that a positive MRI scan for ACL pathology combined with a normal arthroscopy does not necessarily represent a false positive MRI; it may mean that an intrasubstance tear, not grossly detectable, is present.