STUDY DESIGN: A level-3 retrospective cohort analysis. OBJECTIVE: The aim of this study was to describe obesity's effect on complications and outcomes in degenerative spondylolisthesis patients treated by minimally invasive transforaminal lumbar interbody fusion (MI TLIF). SUMMARY OF BACKGROUND DATA: Obesity is associated with a greater complication rate among lumbar spine surgery patients. Poor clinical outcomes might likewise be supposed, but the association is not well established. Minimally invasive techniques have been developed to reduce complications and improve clinical outcomes in comparison to traditional open techniques. METHODS: We reviewed 134 consecutive patients with degenerative spondylolisthesis undergoing MI TLIF. Subjects were grouped into nonobese (N = 65) and obese (N = 69) cohorts. The obese group was further subdivided by BMI. Patient demographics, perioperative complications, and outcome scores were collected over a minimum of 24 months. Four periods (intraoperative, postoperative hospitalization, 6-month, and 24-month postoperative) were assessed. RESULTS: Cohort demographics were not significantly different, but it was noted that obese patients had more major comorbidities than nonobese patients. There was no difference in intraoperative complications between the two groups. The in-hospital complication rate was significantly greater in the obese group. The 6-month postoperative complication rate was not different between cohorts. Wound drainage was most common and noted only in the obese cohort. Complications at 24 months were not different but did trend toward significance in the obese for recurrence of symptoms and total complications. Functional outcome was better among nonobese subjects compared with obese subjects at every interval (significant at 6 and 12 months). Back pain scores were significantly better among nonobese subjects than obese subjects at 24 months, but Leg Pain scores were not different. CONCLUSIONS: MI TLIF can be safely performed in the obese population despite a higher in-hospital complication rate. Knowledge of common complications will help the treatment team appropriately manage obese patients with degenerative spondylolisthesis. LEVEL OF EVIDENCE: 3.