Low back pain and radiating pain in the leg are the main symptoms of the spondylolisthesis and various surgical treatments are recommended after having enough conservative treatments. The spinal fusion in situ either posterior, posterolateral or anterior route is the usual method for symtomatic spondylolisthesis or to prevent progression of slipping but the neurogenic symptoms in the legs are not well solved, so the decompression procedures are necessary. The authors reviewed 26 cases of isthmic spondylolisthesis having low back pain and sciatica which are operated during the 10 years since 1973 at Fatima Hospital and the followings are obtained. 1. There were 15 males and 11 females with ages from 18 years to 63 years having average 40.1 years. 2. The displaced vertebrae were 5th lumbar in 18 and 4th lumbar in 8 cases and the degree of displacement was Grade I in 14, Grade II in 10, Grade III in 1 and no slipping in 1 case. 3. The types of surgery were decompression and H-graft in 22, simple posterior fusion in 3 and Gll's procedure in 1 case. 4. The laminas were considerably loose in all cases and there were small fibrous mass at the pars area in half of the cases. .5. The spine became very stable immediately after H-grafting and the intervertebral foramen became widened freeing nerve root. 6. Bony union obtained in 88% and satisfactory result in 85% at the follow-up from 6 months to 7 years and 2 months with average 1 year and 7 months. 7. The decompression is necessary for the radiating pain in the leg and H-grafting is satisfactory and simple procedure after decompression laminectomy.