Abstract Background Context Obesity's impact on standing sagittal alignment remains poorly understood, especially with respect to the role of the lower-limbs. Given energetic expenditure in standing, a complete understanding of compensation in obese patients with sagittal malalignment remains relevant. Purpose This study compares obese and non-obese patients with progressive sagittal malalignment for differences in recruitment of pelvic and lower limb mechanisms. Study Design/Setting Single center retrospective review. Patient Sample 554 patients (277 obese, 277 non-obese) identified for analysis. Outcome Measures Upper body alignment parameters: sagittal vertical axis (SVA) and T1 spino-pelvic inclination (T1SPi). Compensatory lower-limb mechanisms: pelvic translation (PS: pelvic shift), knee (KA) and ankle (AA) flexion, hip extension (SFA: sacrofemoral angle), and global sagittal angle (GSA). Methods Inclusion criteria were patients≥18 years that underwent full body stereographic x-rays. Included patients were categorized as non-obese (N-Ob: BMI<30 kg/m2 ) and obese (Ob: BMI≥30 kg/m2 ). To control for potential confounders, groups were propensity score matched by age, gender and baseline pelvic incidence (PI), and subsequently categorized by increasing spino-pelvic (PI-LL) mismatch: <10°, 10°-20°, >20°. Independent t-tests and linear regression models compared sagittal (SVA, T1SPi) and lower limb (PS, KA, AA, SFA, GSA) parameters between obesity cohorts. Results 554 patients (277 Ob, 277 N-Ob) were included for analysis, and were stratified to the following mismatch categories: <10°: n=367; 10°-20°: n=91; >20°: n=96. Ob patients had higher SVA, KA, PS and GSA compared to N-Ob (p<0.001 all). Low PI-LL mismatch Ob patients had greater SVA with lower SFA (142.22° vs. 156.66°, p=0.032), higher KA (5.22° vs. 2.93°, p=0.004) and PS (4.91 vs. -5.20 mm, p<0.001) compared to N-Ob. With moderate PI-LL mismatch, Ob patients similarly demonstrated greater SVA, KA, and PS, combined with significantly lower PT (23.69° vs. 27.14°, p=0.012). Obese patients of highest (>20°) PI-LL mismatch showed greatest forward malalignment (SVA, T1SPi) with significantly greater PS, and a concomitantly high GSA (12.86° vs. 9.67°, p=0.005). Regression analysis for lower-limb compensation revealed that increasing BMI and PI-LL predicted KA (r2 =0.234) and GSA (r2 =0.563). Conclusions With progressive sagittal malalignment, obese patients differentially recruit lower extremity compensatory mechanisms while non-obese preferentially recruit pelvic mechanisms. The ability to compensate for progressive sagittal malalignment with the pelvic retroversion is limited by obesity.