Clinical diagnosis of lateral collateral ligamentous injury caused by ankle sprains depends primarily on clinical signs, and X-ray and CT images. None of these, however, provide direct or accurate information about ligamentous injury. MRI has long been testified as a useful tool in the demonstration of ligaments due to its good resolution of soft tissues. We confirmed the appearance of the lateral collateral ligaments of the ankle joints on MR images by comparing MR images with CT images of the ligaments enhanced by coating with contrast medium after dissection of six cadaver feet. Compare study of MR images reveals no difference in the natural position and the dorsal position (P > 0.05), whereas, taken into the consideration the long hour of MRI examination, the natural position is regarded as the optimal position for MRI performance. Measured on transverse MR images, lateral ligaments of acutely injured ankles were significantly thicker than those of normal ankles (P < 0.01). According to the MR images of normal and injured ankles, the lateral collateral ligaments injuries were classified as type I and type II. Osteal contusion, cartilaginous injury, musculotendinous injury, tenosynovitis, and peritenosynovitis were also observed by MRI in type I and type II acute lateral collateral ligament injury. All these complications have higher incidence in type II than in type I injury (P < 0.05). Thus, by comparing with the CT images and the anatomy we confirmed the normal appearance of the lateral collateral ligaments on MR images and figured out that the natural position is the optimal position for MRI performance. The thickness of the ligaments and incidence of the complications could be regarded as useful cue for the assistant in clinical diagnosis of the lateral collateral ligament injury.