Summary:Two cases are presented, both males with severe total spondylolisthesis and both with Marfan's syndrome. One was treated by decompression and posterolateral fusion and the other by decompression, posterolateral fusion, reduction by halo‐femoral traction, and then anterior fusion. Both had excellent results in terms of pain relief and relief of severe hamstring tightness. One patient subsequently died of a dissecting aneurysm. A relationship between Marfan's syndrome and spondylolisthesis is strongly suggested.