Between 1979 and 1996, 40 patients with high-grade lumbosacral spondylolisthesis were treated in our institution using a newly designed osteosynthesis device. The mean age was 13 years and 6 months, and the mean follow-up was 18 years. Combined posterior decompression and anterior reduction, instrumentation and fusion of the slippage were performed in all cases. The technique includes reduction of the slippage by means of an anteriorly placed plate that engages two screws, previously placed during the posterior approach, going through the S1 vertebra. Progressive compression applied on the plate by the screws achieves reduction. Complete fusion was obtained in all 40 patients. Twelve patients presented a postoperative radiculopathy, from which only ten recovered completely. There were six L4-L5 annulus lesions, responsible for instability, produced by the plate. We report five late infections. Thirty-five of the forty patients were asymptomatic at the latest follow-up. The double compressive plate technique proved to be effective in obtaining lumbosacral fusion and optimal slippage reduction. However, the high rates of neurological and infectious complications preclude recommendation of this technique in its present form.