Cauda equina syndrome (CES) is a rare syndrome that has been described as a complex of symptoms and signs--low back pain, unilateral or bilateral sciatica, motor weakness of lower extremities, sensory disturbance in saddle area, and loss of visceral function--resulting from compression of the cauda equina. CES occurs in approximately 2% of cases of herniated lumbar discs and is one of the few spinal surgical emergencies. In this article, we review information that is critical in understanding, diagnosing, and treating CES.