It is often difficult for the radiologist to determine if a given sacral meningeal cyst is causing symptoms. Radiographic criteria for identifying cysts likely to be symptomatic are needed. Using conventional magnetic resonance (MR) imaging along with a specifically designed flow-sensitive sequence, the authors characterized 24 cysts (19 patients) with respect to diameter and communication with the subarachnoid space. They found no significant difference in size between symptomatic and asymptomatic cysts (P > .05) but did observe a clear-cut disparity in the context of communication: Five of five asymptomatic cysts were shown to communicate on MR flow studies, while seven of seven symptomatic cysts were not shown to communicate. The authors propose that flow-sensitive MR imaging is useful in differentiating communicating from noncommunicating sacral meningeal cysts and that this information may be of value in classifying these lesions as more or less likely to be symptomatic.