This study aimed to identify risk factors for major adverse events (AEs) after lumbar fusion surgery in patients aged 75 and over and evaluate the role of several common geriatric comprehensive assessment items in predicting postoperative major AEs.This is a prospective cohort study of patients aged ≥75 years who underwent open lumbar fusion for degenerative spine disease from August 2019 to August 2022. The primary outcome measure was the incidence of major postoperative AEs within 90 days after surgery. Clavien-Dindo III-IV complications and unplanned readmission were defined as major AEs. Patients' characteristics, laboratory tests, assessment results, and surgery-related variables were compared between the major AEs and the non-major AEs groups. Multivariable logistic regression analysis was used to identify independent risk factors for major AEs. The logistic regression model was evaluated in another prospective cohort of patients from October 2022 to October 2023.A total of 301 patients (mean [SD] age, 79.7 [3.5] years; 60.5% male) were included in the study. Five features, including female (OR 1.99, p = 0.040), higher body mass index (BMI) (OR 1.090, p = 0.024), frailty (OR 2.043, p = 0.032), hypoalbuminemia (OR 2.489, p = 0.040), and higher Charlson comorbidity index (CCI) (OR 1.397, p = 0.024), were independently associated with major AEs and were selected to develop a predictive nomogram of major AEs. The area under the curve values for the development set and validation set were 0.75 and 0.71, respectively.Preoperative frailty, hypoalbuminemia, female sex, greater BMI, and higher CCI grade were risk factors for 90-day major AEs after lumbar fusion surgery in older patients. The predictive nomogram that we developed using this data can enhance preoperative risk counseling and optimization for older patients.Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.