OBJECTIVE. Myxopapillary ependymomas are highly vascular tumors that arise almost exclusively in the thoracolumbar region and produce symptoms that may mimic discogenic pathology. The purpose of our study was to define the typical MR features of myxopapillary ependymoma and to determine the value of MR imaging in identifying the tumor, establishing its extent, and defining its relationship to intraspinal structures. MATERIALS AND METHODS. MR studies performed on 20 patients (13 men and seven women; mean age, 35 years) with 24 pathologically proven myxopapillary ependymomas were evaluated retrospectively for size and location of lesions, expansion of the central spinal canal and neural foramina, and MR signal characteristics and enhancement patterns. T1-weighted (16 patients), proton density-weighted (15 patients), T2-weighted (14 patients), and enhanced T1-weighted (nine patients) sequences were examined. RESULTS. In all patients, masses were detected on MR images. MR imaging defined solitary masses in 17 patients and multiple lesions in three. Of the 24 tumors, MR imaging characterized 21 as predominately intradural extramedullary, two as intramedullary and intradural extramedullary, and one as extradural postsacral. Two lesions had associated syrinxes. Lesions occurred most often at the level of the L2 vertebral body, and no tumor extended above T9. Tumors spanned an average of four vertebral segments. MR imaging showed expansion of the spinal canal in five of eight tumors that extended over five or more vertebral segments. Two tumors extended into the neural foramina. The T1-weighted signal of the tumor was isointense in 12 patients, hypointense in three patients, and hyperintense in one patient. The T2-weighted signal was always hyperintense. All tumors imaged after administration of IV contrast material showed enhancement. CONCLUSION. MR imaging was valuable in identifying the extent of tumors and in defining their relationship to the intraspinal structures. Although the MR findings in myxopapillary ependymoma are nonspecific, the diagnosis can be suggested by s large, intensely enhancing, intradural extramedullary thoracolumbar mass that extends for several vertebral levels. Imaging protocols should examine the entire thoracolumbar region and include IV contrast.