A 33-year-old man presented with a rare case of lumbar epidural venous varix causing radiculopathy manifesting as sciatica exacerbated during bowel movements. The left straight-leg raising test was positive and patellar tendon reflex was lost. Lumbar magnetic resonance imaging showed a mass lesion in the epidural space at the L4 level just anterior to the dural sac on the left, appearing as hypointense on T(1)- and hyperintense on T(2)-weighted images, with ring-like enhancement with gadopentetate dimeglumine. He underwent surgery under a preoperative diagnosis of cystic nerve sheath tumor. After left hemilaminectomy, intraoperative ultrasonography showed a low echoic mass lesion ventral to the L4 nerve root. The mass was dark blue with a smooth wall. Tearing of the wall resulted in continuous bleeding. After removal of the lesion, we confirmed that the dura of the nerve root was intact. Histological examination of the surgical specimen confirmed venous tissue. The postoperative course was excellent. Lumbar epidural varix is difficult to diagnose preoperatively. Lumbar epidural varix should be considered if the lesion is smaller on preoperative than intraoperative imaging, or disappears with bleeding cessation, as this may avoid unnecessary widening of the operative field. The correct preoperative diagnosis remains difficult, so we recommend surgical removal and histological confirmation.