Sacral meningeal cyst is usually asymtomatic, but may be responsible for sciatic pain syndromes and other clinical symptoms. Sacral meningeal cyst might be suspected when definite explanation for the clinical symptom, such as herniation of the intervertebral disc or spinal stenosis is not found. Plain films and CT may suggest the presence of sacral meningeal cyst, but MR is the current imaging study of choice. Evaluation of the correlation between the symptom and the cyst is as important as detection of it. We have experienced a case of sacral meningeal cyst detected during caudal epidural block. The patient complained of low back pain radiating to thigh. Plain films and lumbar spine CT showed no remarkable finding except disc bulging. During caudal epidural needle insertion, there was leakage of clear CSF, and intrasacral cystic shadow was visualized by dye injection. MR confirmed sacral meningeal cyst.