Objective To investigate the cl inical outcomes of lumbar spondylol isthesis associated with lumbar spinal stenosis through decompressive laminectomy, spondylol ithesis reduction system (SRS) internal fixation, single posteriolateralVigor Spacer threaded fusion cages and intertransverse process arthrodesis bone grafting. Methods From June 2002 to June 2006, 58 cases of lumbar spondylol isthesis were treated with decompressive laminectomy, fixed by SRS instrumentation, posterior installed with interbody Vigor Spacer Cage and bone grafted between intertransverse process arthrodesis. There were 47 males and 11 females, aged 32-66 years old (45.8 on average). The course of disease was 3 months to 7 years, with an medium course of 25 months. Accoding to the Meyerding standard, 38 cases were classified as degree I and 20 as degree II. Spondylol isthesis between L4 and L5 covered 21 cases and between L5 and S1 covered 37 cases. There were 44 cases of lumbar spondylol isthesis and 14 of degenerative lumbar spondylol isthesis. The intervertebral height was 1.5-10.5 mm with the average of 5.1 mm. Results All patients’ incisions obtained heal ing by first intension after operation. The operation time was 50-90 minutes with an average of 65 minutes. The blood loss was 200-500 mL with an average of 250 mL. The patients were followed up for 10-38 months with an average of 23.6 months. According to the Macrab criteria, 54 cases were excellent, 3 good, 1 fair and the choiceness rate was 98.3%. According to the Meyerding classification, 38 cases of degree I and 19 out of 20 cases of degree II obtained complete reduction, and the rate of complete reduction was 98.3%. There were 57 (98.3%) cases which fused well 3-6 months after operation. The intervertebral height resumed to 9.6-12.5 mm with an average of 11.6 mm, and no intervertebral height loss was found. Conclusion The treatment of lumbar spondylol isthesis with decompressive laminectomy, SRS internal fixation, single posteriorolateral Vigor Spacer threaded fusion cage and bone grafting has excellent cl inical results and stable reduction.