Researchers conducted a cohort study that looked back. For an investigation, they sought to determine the complication rates after surgical treatment for symptomatic degenerative and isthmic spondylolisthesis and the relationship between slip reduction and complication rates. Investigators conducted a retrospective cohort study of adult fusion patients with degenerative or isthmic spondylolisthesis who had 1-level and 2-level fusions. The degree of decrease and complications were calculated, and complication rates were compared between those who reduced and those who did not. In 56.5 % of the 140 patients included in this study, the surgical reduction was improved by 1 Meyerding grade. About 60%  of the patients had a grade 1 spondylolisthesis. Furthermore, 62.5% of grade 2 slips improved by 1 degree. In comparison to in situ fusion, surgical reduction during lumbar fusion did not result in a greater rate of problems. In the retrospective case series, a 1-grade decrease of the slip was obtained in 56% of patients undergoing 1-level or 2-level lumbar fusion for degenerative or isthmic spondylolisthesis. Compared to in situ fusion, reducing the spondylolisthesis did not result in a higher rate of complications.