The methods of treatment of spondylolisthesis range from posterior fusion to instrumentation, and circumferential fusion. Combined anterior and posterior fusion with instrumentation had been carried out in one or two stages and satisfactory results were obtained in nighteen cases with follow-up period of one year to four years at department of orthopedic surgery of Ewha Womans University Hospital from 1987 to 1991. The results were as follows: 1. Of 19 patients, 7 patients were male and 12 patients were famale. 2. The isthmic type was 12 cases (63.1%) and the 5th lumbar vertebral involvement is common (12 cases, 63.1%). 3. The operative treatment was as follows: Posterior fusion with instrumentation was 8 cases, and anterior fusion with instrumentation was 11 cases. 4. The combined anterior and posterior fusion with instrumentation had been carried out in one stage operation at 8 cases, and two stage operation was done at 11 cases. 5. The average operation time was 3.0 hrs in one stage operation, 3.1 hrs in two stage operation, and the average amount of blood loss was 22cc/Kg in one stage, 17cc/Kg in two stage. 6. The satisfactory results were obtained in 19 cases, but there was no specific difference between one stage and two stage operation.