Using a new surgical regimen, fourteen patients with lumbosacral spondylolisthesis and more than 50 per cent slipping were treated by reduction of the slip with two Harrington distraction rods extending from the first lumbar laminae to the sacral alae and bilateral posterolateral fusion from the fourth lumbar to the second sacral segment. Then, at a second procedure, thirteen had an anterior lumbosacral fusion using two bicortical wedge-shaped iliac grafts. The distraction rods were removed six to twelve months later. At follow-up, correction of the slips ranged from 70 to 100 per cent. In four of the thirteen patients the reduction was improved by 10 to 13 per cent during the anterior procedure. In one patient, a twenty-one-year-old women with a slip of more than 100 per cent, a cauda equina syndrome developed after the reduction and posterolateral fusion, and this necessitated removal of th rods and cancellation of the anterior fusion. This patient recovered completely and her final result was a solid posterolateral fusion in situ, with her abnormal posture and gait unchanged. The other thirteen patients, after follow-up ranging from two years to six years and seven months, had solid fusion, normal spinal alignment, normal anatomy of the spinal canal, and normal posture and gait. Only one patient had loss of correction during follow-up, which amounted to 7 per cent. We concluded that correction of severe spondylolisthesis (50 per cent or more) in properly selected patients can be accomplished by this two-stage procedure without risk of further slipping, pseudarthrosis, persistent deformity, or recurrence of the slip due to late remodeling.