The most common corrective surgery for adolescent idiopathic scoliosis (AIS) is posterior instrumented spinal fusion, which is a relatively lengthy procedure. Longer procedures are known to have higher rates of negative outcomes and higher economic costs across the surgical specialties. The purpose of this study is to identify the factors that influence the length of this operation in AIS patients. This was an institutional review board-approved, retrospective cohort study. All primary posterior instrumented arthrodesis procedures in 2011–2013 performed by three surgeons on AIS patients at a tertiary care hospital were included. Age, race, sex, BMI, Cobb angle, curve flexibility, Lenke classification, number of levels fused, number of screws used, osteotomy use, intraoperative O-arm use, and length of surgery (time from incision to closure) were obtained from the electronic medical record. Multivariable linear regression analysis was used to determine independent predictors of length of surgery, and standardized regression coefficients were calculated to compare the relative magnitude of significant variables. A total of 95 procedures were included. The average length of surgery was 375±72.7 min. The multivariable linear regression analysis contained the variables Cobb angle, number of screws used, osteotomy use, Lenke curve type, surgeon, patient age, and sex. The regression identified the number of screws used [β=4.72, P=0.003, 95% confidence interval (CI) 1.7–7.8], osteotomy use (β=50.2, P=0.004, 95% CI 16.2–84.1), Lenke type 3 curve (β=77.9, P=0.001, 95% CI 31.7–174), male sex (β=62.5, P=0.003, 95% CI 21.5–103), the Cobb angle (β=1.04, P=0.045, 95% CI 0.02–2.1), and the surgeon (β=75.2, P<0.0001, 95% CI 40–110) as independently associated with the length of surgery. The most significant factor associated with operative duration was the surgeon performing the case. We identified male sex, number of screws used, Lenke type 3 curves, osteotomy use, Cobb angle, and the surgeon variable as significantly associated with increased length of surgery in posterior arthrodesis of AIS patients.