We report on 2 patients in whom a cystic dilation of the conus medullaris was incidentally found at MR imaging carried out in the work-up for sciatica. The cysts were well circumscribed and had signal intensity identical to the CSF on both T1- and T2-weighted images. There was no evidence of contrast enhancement. None of the patients had specific symptoms related to the spinal cord. At surgery, no evidence of malignancy was seen in any of the patients. A benign cystic dilation, also called dilated ventriculus terminalis, occasionally can be seen in the conus medullaris as an incidental finding at thoracolumbar MR imaging. Unless the expansion per se indicates cyst drainage, these patients may be monitored by clinical and MR follow-up, avoiding surgery in a substantial number of cases.