Osteochondral lesions (osteochondritis dissecans) of the talus are common articular lesions that are usually traumatic in origin. Clinical management of these lesions is based on whether or not the fragments are attached. We studied the value of MR imaging in determining the stability of the osteochondral fragments. In 13 of 14 patients who had had correlative surgery, we accurately predicted the presence and extent of attachment of the fragment to the talus by performing preoperative MR imaging. The other patient had a false-positive diagnosis of a chondral fragment. All seven partially attached fragments had an irregular high-signal zone on T2-weighted images at the fragment/talar interface. The four unattached fragments had a complete ring of fluid surrounding the lesion. On the basis of these findings, we think MR of the ankle can be used to assess accurately talar osteochondral lesion stability and aid in clinical decision making.