Objective To identify factors that account for variation in complication rates across hospitals and surgeons performing lumbar spinal fusion surgery. Data sources Discharge registry including all non-federal hospitals in Washington State from 2004–2007. Study Design We identified adults (n = 6,091) undergoing an initial inpatient lumbar fusion for degenerative conditions. We identified whether or not each patient had a subsequent complication within 90 days. Logistic regression models with hospital and surgeon random-effects were used to examine complications, controlling for patient characteristics and comorbidity. Principal findings Complications within 90 days of a fusion occurred in 4.8% of patients, and 2.2% had a reoperation. Hospital effects accounted for 8.8% of the total variability, and surgeon effects account for 14.4%. Surgeon-factors account for 54.5% of the variation in hospital reoperation rates, and 47.2% of the variation in hospital complication rates. The discretionary use of operative features, such as the inclusion of Bone Morphogenetic Proteins, accounted for 30% and 50% of the variation in surgeons’ reoperation and complication rates, respectively. Conclusions To improve the safety of lumbar spinal fusion surgery, quality improvement efforts that focus on surgeons’ discretionary use of operative techniques, may be more effective than those that target hospitals.