Elective fusions for degenerative spine disease have increased over the past two decades in the USA, with variability in complications and hospital costs. The additional service costs associated with adverse perioperative events remain unknown. Our objective is to improve understanding of trends in safety and cost of elective lumbar fusions on a national scale.A weighted sample of 1,526,386 adults undergoing elective lumbar fusion for degenerative indications were identified in the National Inpatient Sample (NIS) years 2002-2014. Twelve categories of major complications by system, and patient/hospital variables, were evaluated as predictors of the overall reimbursed cost. Mean differences (B) and 95% confidence intervals [95% CI] are reported. Significance is assessed at P<0.001.Nineteen percent of patients experienced inpatient complication. After adjusting for inflation, the mean overall cost was $ 32,802±19,557. Costs increased with presence of each of the 12 categories of complications, and by number of levels fused. Rates of most frequent complications and their adjusted cost-of-care were acute postoperative anemia (11.2%, B=$ 1817 [$ 1722-1913], P<0.001), renal/urinary (1.9%, B=$ 510 [$ 288-732], P<0.001), pulmonary (1.8%, B=$ 6014 [$ 5785-6243], P<0.001) and gastrointestinal (1.8%, B=$ 3699 [$ 3490-3908, P<0.001). The costliest adverse events were infection (B=$ 15,882 [$ 15,424-16,339], P<0.001), thromboembolism (B=$ 8856 [$ 8400-9311], P<0.001), hematoma/seroma/vascular (B=$ 8050 [$ 7784-8316], P<0.001).The number of elective lumbar fusions for degenerative spine disease increased 276% in the USA from 2002-2014 with growing surgeon preference for lateral techniques, and an increasing proportion of combined anterior and posterior approaches. Overall complication rates decreased from 2002-2014, despite an older patient population. After adjusting for inflation, cost was relatively stable across years 2002-2014. Complications by system were associated with increased cost, underscoring the need to address so...