All the surgical procedures will be performed by a single surgeon (J. P.). The patients is positioned prone on the Relton-Hall frame after general anesthesia. Decompression is done under the endoscope with the tubular retraction system METRx (Medtronics, Minneapolis, MN). For patients with unilateral neurological symptoms, we will perform unilateral laminotomy and foraminotomy. For patients with bilateral neurological symptoms, we will performe unilateral laminotomy for bilateral decompression (ULBD) to decompress the central canal and bilateral lateral recesses.