Adult patients with high-grade spondylolisthesis not responding to nonoperative treatment can be stabilized in situ with posterior instrumentation from L4 to S1. The use of adjunctive fixation with iliac screws and/or transvertebral screws is recommended for the adult patient, particularly in revision or unstable cases. Reduction of the slipped vertebrae remains controversial for all grades of spondylolisthesis and more so for the adult patient. Partial reduction of the slip angle, decreasing the lumbosacral kyphosis, should be considered if significant sagittal malalignment is present or to improve arthrodesis success. Anterior column support should be performed, particularly when reduction has been obtained. Anterior column support can be performed, anteriorly or posteriorly, either by using inter vertebral body structural strut support or with a transsacral fibular dowel to improve stability and success of arthrodesis.