Methods: Inclusion criteria: ≥5-level fusion, sagittal/coronal deformity, and minimum 2-year follow-up. Primary outcomes were the highest quartile of EBL (mL), operative time (minutes), and LOS (days). EBL was calculated based on the hemoglobin drop. Bivariate analysis and multivariable logistic regression were performed, controlling for age, comorbidities, and preoperative radiographic parameters. Results: Among 238 patients (mean age, 63.4±17.4 years), the highest EBL quartile (2,594.0±1,550.5 mL) had more three-column osteotomies (3CO) (30.5% vs. 14.8%, p=0.008). Multivariable predictors of highest EBL were older age (odds ratio [OR], 1.03; p=0.039) and 3CO (OR, 3.60; p=0.007). The highest operative time quartile (618.9±99.4 minutes) had more 3CO (27.1% vs. 15.3%, p=0.041) and higher rod fracture rates (30.5% vs. 15.8%, p=0.014). Multivariable predictors of the highest operative time were higher total instrumented levels (TIL) (OR, 1.26; p<0.001) and older age (OR, 1.05; p=0.003). The highest LOS quartile (14.5±18.5 days) had more 3CO (27.3% vs. 14.3%, p=0.045). The multivariable predictor of highest LOS was higher TIL (OR, 1.23; p<0.001). Conclusions Three-column osteotomy was the strongest predictor of perioperative morbidity in ASD surgery, consistently associated with higher blood loss, longer operative times, and prolonged hospital stays. Recognizing its impact can inform surgical strategies to improve patient outcomes.