Background: Isthmic spondylolisthesis is a common cause of low back pain in adolescents. Spinal fusion is the key element in the surgical treatment of low grade isthmic spondylolisthesis. Spinal fusion can be achieved by posterolateral fusion (PLF) or circumferential fusion. The three techniques traditionally used for circumferential fusion include anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF). Patient and methods: 50 patients with low grade isthmic spondylolisthesis were managed with spinal fusion at the Zagazig university hospital. Patients were divided into two groups: group I included patients managed by TLIF and group II included patients managed by PLF. The mean age of patients was 34.6 years (range: 26 - 43 years) in group I and 36.8 years (range 28 – 46 years) in group II. Sex distribution was 9 males and 16 females in group I and 7 males and 18 females in group II. Exclusion criteria included: patients with high grade spondylolisthesis, traumatic spondylolisthesis, degenerative spondylolisthesis, neoplastic spondylolisthesis, patients with acute or chronic infection, and congenital malformation. Results: no patients were dropped in the follow-up. In both groups, the mean VAS for back pain and leg pain and the ODI showed statistically significant difference between the values obtained preoperatively and the values obtained at the one-year follow-up visit. In comparison between both groups for the change in the VAS for back and leg pain and ODI score, group I showed a significant difference regarding the reduction in the VAS for back pain compared to group II. However, the difference in the VAS for leg pain and ODI was not statistically significant. Conclusion: Both TLIF and PLF are effective options for the treatment of low grade isthmic spondylolisthesis in adults. However, TLIF gives better clinical outcome and higher fusion rate, as a result, it is a better option.