Background Context: Postoperative delirium is a clinically significant acute disorder of consciousness especially prevalent in older adult patients, of which more than 100,000 per year undergo spinal fusion surgery. There are no proven preventative therapies, and delirium is associated with increased postoperative complications, functional decline, morbidity, and mortality. Purpose: To identify perioperative risk factors for postoperative delirium (POD) after lumbar spinal fusion procedures in patients aged 65 or older. Study Design: Retrospective Review Patient Sample: 702 patients who underwent lumbar spinal fusion surgery from 11/13/2017 to 1/30/2021. Outcome Measures: The primary outcome was the presence of postoperative delirium assessed by the Delirium Observation Screening Scale (DOSS) and Confusion Assessment Method for the ICU (CAM-ICU). Methods: Demographic, surgical, and perioperative data were obtained from the electronic medical records. The primary outcome was presence of postoperative delirium. Univariate and multivariate analyses were performed. A binomial logistic regression model was designed using a custom written MATLAB script. Results: Of the 702 patients included in the study, 173 (24.6%) developed POD. Our analysis revealed that older age (p < 0.001), lower preoperative hemoglobin (p < 0.001), and higher ASA grade (p < 0.001), were significant preoperative risk factors for developing POD. The only significant intraoperative risk factor was a higher number of spinal levels that were instrumented (p < 0.001). Higher pain scores on postoperative day 1 (p < 0.001), and lower postoperative hemoglobin (p < 0.001) were associated with increased POD; as were ICU admission (p < 0.001) and increased length of ICU stay (p < 0.001). Patients who developed POD had a longer hospital stay (p < 0.001) with lower rates of discharge to home as opposed to an inpatient facility (p < 0.001). Conclusions: Risk factors for older adults undergoing lumbar spinal fusion surgery include advanced age, lower preoperative and postoperative hemoglobin, higher ASA grade, greater extent of surgery, and higher postoperative pain scores. Patients with delirium had a higher incidence of postoperative ICU admission, increased length of stay, decreased likelihood of discharge to home and increased mortality, all consistent with prior studies. Further studies will determine whether adequate management of anemia and pain lead to a reduction in the incidence of postoperative delirium in these patients.