PURPOSE: This study aimed to compare sagittal spinal parameters between healthy adolescents and those with adolescent idiopathic scoliosis (AIS), identify factors influencing disease progression, and provide insights for optimizing preoperative assessments. METHODS: Sagittal full-spine radiographs from 40 healthy adolescents and 41 AIS patients (aged 10-18 years) were analyzed using Mimics 21.0 software. Fifteen parameters, including spinopelvic angle (SPA), thoracic kyphosis (TK), lumbar lordosis (LL), and pelvic tilt (PT), were measured. Statistical analyses included logistic regression to identify predictors of AIS and sex-based subgroup comparisons. RESULTS: SPA was significantly higher in AIS patients compared to controls (median: 176.48° vs. 169.64°, P = 0.008) and emerged as the sole predictor of AIS (odds ratio = 1.568, 95% CI = 1.129-2.177, P = 0.007). Sex differences revealed higher spinal tilt (ST) in female AIS patients (P = 0.034), while males exhibited elevated TK (P = 0.006) and SPA (P = 0.002). Correlations among parameters highlighted strong associations between LL and pelvic incidence (PI, r = 0.682) and between SPA and pelvic tilt (PT, r=-0.537). CONCLUSION: Increased SPA is a critical indicator of AIS, necessitating preoperative evaluation of sagittal spinopelvic alignment. Female patients require heightened attention to spinal tilt. Future studies should expand sample sizes and integrate multi-planar analyses to refine clinical strategies.