Abstract: Objective To investigate the gravitational effect on coronal curvature and vertebral rotation using 3-D ultrasound in patients with adolescent idiopathic scoliosis (AIS). Methods Sixteen female patients with AIS were recruited and examined using a 3-D ultrasound unit incorporated with SonixGPS system (Ultrasonix Medical Corporation, Canada). Ultrasound scanning was performed continuously along the coronal plane from C7 to S1, with a standing and a supine position, respectively. Coronal curvature and vertebral rotation were measured using the center of laminae (COL) method. Multivariate linear regression models were established to determine factors associated with changes of lateral curvature and vertebral rotation in different posture positions. The correlations of measurements between standing and supine were tested using Pearson correlation analyses. Results Changes of coronal curvature and vertebral rotation from a supine to a standing posture were within 1.9°-11.7° and 0.0°-5.9°, respectively. The changes increased with the severity of AIS. The 3-D ultrasound measurements of lateral curvature and vertebral rotation were highly correlated. Conclusion 3-D ultrasound can reveal changes of coronal curvature and vertebral rotation from a supine to a standing posture in patients with AIS, which increase with the severity of AIS. Further studies in large samples are warranted.