To study the contribution of the special morphological features of lumbo-sacral spine as causes of the slipping in the spondylolisthesis, the roentgenographic measurements were performed in 47 cases of spondylolysis, 77 of spondylolisthesis and 597 of several low back pain as a control.

The transitional lumbo-sacral spine was more frequently seen in the spondylolisthesis group, but there was no d ifference between the spondylolysis and control.

The angle between the superior surface and the posterior border of the sacral vertebral body (posterior superior sacral angle) was apparently low in the spondylolisthesis, whereas no difference was noted between another groups.

In conclusion, special morphological features such as low prices of the posterior superior sacral angle is considered one of the risk factors for the cause of slipping.