A 70-year-old man developed pain and functional weakness in the lower limbs with dysesthesia and urinary retention after subarachnoid anesthesia with 0.5% hyperbaric bupivacaine. Neurological and electrophysiological tests and follow-up, as well as diagnostic images (CAT and MR), ruled out spinal cord lesions. The diagnosis was cauda equina syndrome. Cauda equina syndrome is a neurological complication of subarachnoid anesthesia. Associated with use of microcatheters for continuous subarachnoid anesthesia and 5% hyperbaric lidocaine, cauda equina syndrome is rare after a single injection of bupivacaine. Although the pathogenesis of cauda equina syndrome is poorly understood, there is agreement on the neurotoxicity of local anesthetics, particularly of 5% hyperbaric lidocaine.