Our study was an attempt to salvage severely unstable posterior lumbar interbody fusions (PLIFs) by using the lateral bilateral intertransverse single-level (floating) fusion. A retrospective review of six patients with failed L4-L5 PLIFs was carried out. These patients underwent reoperation between 2 weeks and 2 years after the initial surgery. All patients had persistent symptoms, including low back pain and sciatica, interfering with activities of daily living. Computed tomography (CT) scans revealed extrusion of the bone plug into the spinal canal in five patients. All six had a nonunion of the PLIF, and three patients had grade 3 or 4 iatrogenic spondylolisthesis caused by the PLIF. The operation involved decompression followed by lateral intertransverse process fusion with autogenous bone graft. All patients were placed in external immobilization after the procedure for 3 months. Follow-up averaged 38.5 months (range, 21-55), at which time five had substantial pain improvement. Five were radiographically fused. One had a second nonunion, which subsequently healed after reoperation with repeat lateral fusion and Luque plate hardware. Our fusion rate was 83% without the use of instrumentation. In conclusion, we recommend the simplistic procedure of lateral bilateral intertransverse process single-level fusion along with liberal external immobilization for the difficult problem of salvage of failed PLIFs.