METHODS Retrospective cohort study. OBJECTIVE The primary aim of this study was to determine the incidence and risk factors for 30-day adverse events after revision posterior lumbar fusion. The secondary aim was to determine the incidence and risk factors for 30-day readmission after revision posterior lumbar fusion. BACKGROUND The need for revision of a lumbar fusion is an unfortunate occurrence, and there is little known about specific risk factors for morbidity and readmission after this procedure. The purpose of this study is to use a large, national sample to identify patient and operative factors that may contribute to the development of these adverse outcomes. METHODS The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database was used to identify patients undergoing revision posterior lumbar fusion from 2005 to 2013. Patient characteristics were tested for association with any adverse event (AAE), severe adverse events (SAEs), minor adverse events (MAEs), and readmission within 30 days postoperatively using multivariate analysis. RESULTS Of the 1287 patients identified, 8.2% had an AAE, 5.6% had an SAE, and 3.2% had an MAE. AAE was independently associated with American Society of Anesthesiologists (ASA) classification ≥3 and operative time ≥310 minutes (P<0.05 for each). SAEs were associated with only ASA classification ≥3 (P=0.047). MAEs were associated with insulin-dependent diabetes, operative time ≥310 minutes, and 3 or more levels of fusion (P<0.05 for all).Sixty-five patients (5.6%) were readmitted. On multivariate analysis, body mass index (BMI) 25-30, BMI 30-35, BMI≥35, ASA classification ≥3, insulin-dependent diabetes, a 2-level fusion, and 3 or more levels of fusion were associated with readmission (P<0.05 for all). CONCLUSIONS In general, longer, more extensive procedures on sicker patients were associated with increased risk of postoperative complications and readmission.