To clarify the natural course of degenerative spondylolisthesis, the progression of disk slippage and clinical symptoms were studied in 35 patients with more than 10 years of follow-up. Progressive slippage was observed in 12 patients (34%). No progression of slippage was noted in patients exhibiting restabilization signs on X-ray film. There was no correlation between the clinical symptoms and progression of slippage. Surgical intervention should be done with the knowledge of the natural course of this disease.