BACKGROUND : Optimal transfusion thresholds have been extensively studied for various surgical procedures; however, no transfusion threshold has been set for patients undergoing complex spine surgery. The aim of this study was to compare postoperative outcomes relative to perioperative hemoglobin (Hb) levels for patients undergoing complex spine surgery for adult spinal deformity and to evaluate impact of blood transfusion timing on clinical outcomes. METHODS : Retrospective chart review of patients with adult spinal deformity undergoing spine surgery lasting >6 hours or involving ≥6 levels of fusion was performed. Patients were divided into 2 cohorts based on whole hospitalization Hb nadir <9.0 g/dL versus ≥9.0 g/dL. RESULTS : Among 104 patients, 55 (52.9%) had Hb nadir <9.0 g/dL. Compared with the cohort with higher Hb nadir, patients with Hb nadir <9.0 g/dL were more likely to be female (84.5% vs. 65.3%, P = 0.016), present with lower preoperative Hb (12.6 [1.5] g/dL vs. 13.8 [1.2] g/dL, P < 0.001), experience greater change in Hb after surgery (4.4 [1.5] g/dL vs. 3.7 [1.5] g/dL, P = 0.030), receive a postoperative blood transfusion (69.1% vs. 44.9%, P = 0.013), and have a longer length of stay (9.1 [4.8] days vs. 6.2 [3.2] days, P < 0.001). CONCLUSIONS : In patients with adult spinal deformity undergoing complex spine surgery, earlier targeted blood transfusions during surgery, rather than in the postoperative period, may lead to improved postoperative outcomes.