The effects of chronic corticosteroid therapy on complications, readmission, and reoperation after posterior lumbar fusion (PLF) remain underinvestigated, and were examined to determine differences in outcomes.We analyzed patients undergoing PLF between 2006 and 2013 using the National Surgery Quality Improvement Program database (NSQIP). Patients taking steroids for a chronic condition were compared with those not taking steroids. Multivariable regression identified factors independently associated with complications, readmission, and reoperation. A risk score was calculated for predicting complications.A total of 8492 patients were identified, of whom 353 used steroids. The patients using steroids were older (mean age, 65.4 years vs. 61.0 years; P < 0.001), were more likely to be female (61.2% vs. 55.1%; P = 0.025), had a higher American Society of Anesthesiologists class (P < 0.001), were less likely to be functionally independent (90.3% vs. 96.5%; P < 0.001), and were more likely to have a history of hypertension (69.1% vs. 58.3%; P < 0.001), diabetes mellitus (21.8% vs. 17.4%; P = 0.033), cardiac disease (74.8% vs. 66.1%; P = 0.001), and/or severe chronic obstructive pulmonary disease (10.5% vs. 4.2%; P < 0.001). The rates of readmission (9.4% vs. 6.0%; P = 0.023), reoperation (6.5% vs. 3.6%; P = 0.004), overall complications (14.5% vs. 9.6%; P = 0.003), and infections (9.6% vs. 5.1%; P < 0.001) were higher in the steroid group. On multivariable regression, steroids were independently associated with overall complications (odds ratio [OR], 1.38; P = 0.044) and infectious complications (OR, 1.65; P < 0.001), but not with medical complications, readmission, or reoperation. Patients with higher risk scores had higher complication rates.The use of corticosteroid therapy is associated with a moderately increased risk of overall complications, but no association was found with readmission or reoperation.