OBJECTIVE To determine the characteristic magnetic resonance (MR) imaging features of multiple sclerosis (MS) that affect the spinal cord. METHODS Sixty-eight patients underwent MR imaging of the cervical and/or thoracic spine. Plaques were analyzed for lesion length, cross-sectional area and location, signal intensity, and morphology. The clinical parameters of MS type, duration of disease, sex, and age were also correlated with these MR imaging findings. RESULTS One hundred twenty-four demyelinating plaques were found in these 68 patients; 38 had more than one plaque. The majority of plaques were two body segments in length or less and peripherally located, and occupied less than 50% of the cross-sectional area of the cord. Plaques associated with cord atrophy were more likely to occur with the relapsing-progressive form of MS. Cord swelling was found only in the relapsing-remitting form of MS. CONCLUSIONS Spinal cord MS plaques are characteristically peripherally located, are less than two vertebral segments in length, and occupy less than half the cross-sectional area of the cord.