BACKGROUND Cauda equina syndrome (CES) refers to a group of symptoms that occur when the nerves in the cauda equina become compressed or damaged. The most common etiology of CES is lumbar intervertebral disc herniation, but CES following lumbar spinal surgery is rare, especially without motor dysfunction. Herein, we illustrate a case of CES that developed as a complication of spinal surgery and to deduce its possible underlying cause. METHODS A 46-year-old man experienced lumbago, bilateral shank pain, and numbness with neurogenic claudication for 3 years due to degenerative lumbar disc herniation and spinal cord stenosis. After a thorough examination to diagnose lumbar spinal stenosis, the patient underwent bilateral decompression and pedicle screw system internal fixation with bone graft. Postoperatively, the patient showed regained strength in his bilateral shanks, and he did not complain of lumbago and shank pain, but CES occurred, which manifested as underpants-type numbness in the perineum without bladder, anal, and motor dysfunction. METHODS CES as a postoperative complication of lumbar stenosis. METHODS The patient underwent bilateral laminectomies, partial facetectomies, and pedicle screw system internal fixation and fusion with bone graft. Postoperatively, the patient performed adequate rehabilitation exercises and was expected to recover spontaneously. RESULTS The symptoms of pain and claudication resolved after 3 weeks in the hospital, but an underpants-type hypoesthesia in the perineum without motor dysfunction developed. The patient experienced full recovery from CES 6 months after surgery. CONCLUSIONS CES as a complication of lumbar spinal surgery is very rare. Excessive sensitivity to the traction of the dural sac was, in our opinion, the most possible cause of postoperative CES in this case. When the nerve root is pulled intraoperatively, it is best not to cross the central line of the spinous process. The plane of the nerve retractor needs to be parallel to the dural sac at the pulling point to reduce the formation of shear force. Most importantly, gentle maneuver is required because sensitivity to the traction of the dural sac varies individually.