BACKGROUND CONTEXT Surgical correction of adult spinal deformity (ASD) is often associated with significant blood loss and coagulopathy. Optimal intraoperative transfusion algorithm remains debatable. Rotational thromboelastometry (ROTEM), a functional viscoelastometric method for real-time hemostasis testing, may allow early identification of coagulopathy, and hence improve transfusion practices during surgery. PURPOSE To investigate the effects of ROTEM-guided therapy on intraoperative estimated blood loss (EBL) and transfusion requirements in patients who underwent pedicle subtraction osteotomy (PSO) for ASD. STUDY DESIGN/SETTING Retrospective chart review of a prospectively maintained, single-center, multisurgeon database. PATIENT SAMPLE Consecutive ASD patients. OUTCOME MEASURES Primary outcomes: intraoperative EBL and total volume of blood product transfused. Secondary outcomes: packed red blood cells (pRBC), platelets, cryoprecipitate, and fresh frozen plasma (FFP) transfused during surgery. METHODS All ASD patients who underwent single-level lumbar PSO with ROTEM-guided transfusion at our institution were matched in a 1:1 ratio to a historical cohort with the conventional clinical and point-of-care (POC) transfusion algorithm. Covariates for matching were age, body mass index, revision operation status, number of instrumented levels, number of transforaminal lumbar interbody fusions, number of Smith-Petersen osteotomies, and preoperative hemoglobin. RESULTS The matched groups comprised 17 patients each, and comparison of baseline demographic and surgical parameters demonstrated more women (p=.04) and a higher total intraoperative dose of intravenous tranexamic acid (TXA) administered (p=.03) in the ROTEM group. Although not significant, EBL was lower in the ROTEM group (3200.00±2106.24vs. 3874.12±2224.22 mL; p=.36), with small-to-medium effect size (Cohen's d=0.31). Prior to adjusting for TXA, ROTEM-based transfusion was associated with lower volume of total blood products transfused (1624.18±1774.79vs. 2810.88±1847.46 mL; p=.02), with medium-to-large effect size (Cohen's d=0.66). This difference was no longer significant after adjustment for TXA (β=−0.18; 95% CI [−1995.78 to 671.64]; p=.32). pRBC and platelet transfusions were comparable between the matched cohorts. The ROTEM group was associated with greater number of cryoprecipitate units (1.24±1.20vs. 0.53±1.01 units; p=.03) and lower FFP (119.76±230.82vs. 673.06±627.08 mL; p CONCLUSIONS Compared to the conventional transfusion criteria, the use of ROTEM-guided transfusion algorithm in lumbar PSO for surgical correction of ASD was associated with greater number of cryoprecipitate units and lower FFP volume transfused. ROTEM-guided transfusion allowed early identification and treatment of hypofibrinogenemia, and aggressive management of this complication may reduce intraoperative EBL and total volume of blood products transfused.