OBJECTIVE Early sacral fracture is an extremely rare complication of instrumented lumbosacral fusion seen in older, osteopenic women. Previous reports have attributed the problem to the use of multisegmental (three or more levels) fixation, with the transfer of stress forces from rigid spinal implants to the sacrum. We report the only case, to the best of our knowledge, of early sacral fracture after a two-level lumbosacral fusion and the only case of early sacral fracture after reduction of spondylolisthesis. METHODS A patient presented with a sudden recurrence of low back and buttock pain a few days after lumbosacral decompression, reduction of L5-S1 Grade II spondylolisthesis, and instrumented L5-S1 fusion, including posterior lumbar interbody fusion. A transverse sacral fracture was found on plain x-rays 4 weeks later. METHODS Symptoms improved with brace therapy and medical treatment for osteoporosis. CONCLUSIONS Early sacral fracture is a rare cause of pain after instrumented lumbosacral fusion. Although the transfer of loads from rigid spinal implants to adjacent segments is particularly problematic for multisegmental fusions, patients with short-segment constructs may also be affected. Active reduction of spondylolisthesis may provide additional adjacent segment stress contributing to this complication.