To measure the prevalence of obstructive lung disease (OLD) among patients undergoing preoperative pulmonary assessment for idiopathic scoliosis.This was a retrospective, descriptive review from clinical data in a tertiary care pediatric hospital in the US. Patients (n = 176) with idiopathic scoliosis with Cobb angles of ≥40 degrees who performed acceptable and repeatable preoperative pulmonary function testing were included. The primary outcome measure was the forced expiratory volume in the first second (FEV 1 )/forced vital capacity (FVC) ratio.The prevalence of OLD (low FEV 1 /FVC ratio) was 39% (68/176 patients). In multivariate modeling, radiographic measures were poor predictors of pulmonary function outcomes of FVC (r 2 0.06), FEV 1 (r 2 0.05), FEV 1 /FVC ratio (r 2 0.08), and total lung capacity (r 2 0.06).OLD is common in patients with idiopathic scoliosis. We recommend preoperative pulmonary function testing for patients with idiopathic scoliosis under consideration for spinal fusion surgery.