For a study, it was determined that the transverse gravitational deviation index (TGDI), which was defined to quantify the transverse plane position of any vertebra with respect to the GL, will be used in the study to investigate the relationship between balance control and health-related quality of life (HRQOL) in patients with adult spinal deformity (ASD). During a preoperative setting, demographic data and balance control were both identified as important determinants of HRQOL in ASD patients. As a result, a greater knowledge of how spinal alignment affects balance is essential. About 15 asymptomatic healthy volunteers (mean age 60.1 ± 11.6 years old) and 55 ASD patients (mean age 63.5 ± 10.1 years old) were included in the study after giving their informed consent. Using General Linear Modeling, the relationship between BESTest performance and the core outcome measures index (COMI) and spinopelvic alignment was investigated (GLM). Statistical significance was defined as a P-value of less than 0.05. After adjusting for confounding demographic characteristics, the L3 TGDI was found to be related to balance control in the overall ASD group (P=0.001; adjusted R2=0.500) and explained 19% of the observed variance in balance performance. Furthermore, despite a substantial influence of age (P=0.020), COMI is associated with L3 TGDI in a subgroup of ASD patients with both coronal and sagittal malalignment of L3 (P=0.027; slope B=0.047). The distance component of the L3 TGDI, that is, the offset between the center of the L3 vertebral body and the GL in the transverse plane was associated with both the level of balance impairment and HRQOL in ASD patients with a combined coronal and sagittal malalignment of the L3 vertebra.