Degenerative spondylolisthesis, introduced by Newman and Stone in 1963, is a forward slipping of a lumbar vertebrae with an intact neural arch and causes a segmental stenotic condition of the spinal canal. The chrateristics of the degenerative spondylolisthesis is that the enlarged and hypertrophied posterior articular processes protrude not only posteriorly but also into the spinal canal with resultant narrowing and posterior joint cartilage and capsule are frequently absent. Generally, degenerative spondylolisthesis occurs at the 4th and 5th lumbar vertebrae and the majority is women. Many surgical methods have been tried, but definite management of degenerative spondylosisthesis still is remained controversial. However, in persistent pain in the lower back, buttocks and thighs, sciatica and progression of displacement, we prefer the surgical intervention to conservative treatment. This paper is based on clinical results and follow up studies for 4 males and 8 females with degenerative spondylosisthesis from January of 1983 to April of 1989 who were surgically treated by facetectomy and posterolateral fusion in situ at our hospital. Clinically, 10 out of 12 patients showed excellent and good results at the end of follow up. From the results, we concluded that the facetectomy and posterolateral fusion in situ is a desirable surgical treatment in the degenerative spondylosisthesis.