The scoliosis assessment on both the coronal and sagittal planes is as least as necessary. However, it has a healthy risk to take X-ray examinations for obtaining both radiographs, especially to teenagers. 3-D ultrasound imaging shows the potential for radiation-free scoliosis assessment. In this paper, we develop a novel projection imaging method to obtain the sagittal visualization of spine anatomy. We, therefore, can get both coronal and sagittal projection images simultaneously from a single ultrasound volume data. The method started with deriving spine curves from coronal images at different depths and constructed a non-plane surface, followed by rendering the sagittal spine visualization using the average blending function. The performance was evaluated on 30 subjects (Age: 13.4pm 5.6) with different spine curvatures. The preliminary result shows that the sagittal projection image can represent spinous processes well, which is comparable with those in the sagittal radiograph. The Cobb angles measured on sagittal X-ray images also had a significant correlation with those spinous angles acquired from ultrasound imaging (r=0.93; p < 0.001). The proposed sagittal projection method can greatly facilitate the 3-D assessment for scoliosis with the use of 3-D ultrasound.