For 23 patients with a surgically proven tear of the medial collateral ligament the findings from magnetic resonance imaging (MRI) of the knee were evaluated retrospectively. MRI revealed the tear in all cases, although when the injury was severe, distinguishing high-grade partial tears from complete tears was difficult. Physical examination had indicated a tear in 22 (96%) of the cases. A high prevalence of associated cruciate and meniscal injuries was seen (in 23 [100%] and 12 [52%] of the cases respectively). Tears of the fibular collateral ligament occurred in 13 (57%) of the patients and at least one bony infraction in 22 (96%); most of the infractions were in the lateral compartment. Infractions of the lateral femoral condyle were frequently geographic (in 14 [70%] of the 20 cases) or impacted (in 5 [25%]). The spectrum of injuries associated with tears of the medial collateral ligament was consistent with the findings of previous studies focusing on cruciate and meniscal abnormalities; the minor variations were likely due to the severity of valgus stress in this sample.