PURPOSE: The purpose of this prospective case series (level II) was to determine the clinical outcomes of anterior SIJ fusion, comparing the outcomes of patients who had prior spinal fusions at any level compared to patients who have not. METHODS: This prospective study included 25 patients who underwent SIJ fusion with anterior plate fixation. All patients had failed non-operative treatment, had a positive Patrick test, and positive response to intra-articular SIJ injections with greater than 50 % pain relief. Patients had follow-up at 3, 6, 9 and 12 months where they completed Oswestry disability index (ODI) and Short Musculoskeletal Functional Assessment (SMFA) surveys. Outcome data are available for 19 patients who completed pre-operative and 12-month follow-up surveys. Their average time of the final follow-up was 1.1 years (range 10-33 months). RESULTS: Significant improvements between pre-operative and the final follow-up in ODI (p = 0.007) and SMFA (p = 0.01) were observed; the ODI assessed outcomes in patients who had previous spinal fusion surgery were significantly worse than those that did not at the final follow-up (p = 0.04). CONCLUSION: Patients who have not undergone prior spinal fusion surgery, regardless of age, gender, and BMI have better outcomes following anterior SIJ fusion.