Recent developments in three-dimensional (3D) ultrasound technologies have made it possible to display 3D ultrasound images in real time. 3D ultrasound image data acquired using a mechanical 3D dynamic (4D) probe or a two-dimensional (2D) matrix array probe are resampled and reconstructed to generate 3D ultrasound images. This paper describes the principles and effectiveness of such 3D visualization methods. There are two basic 3D visualization methods: the multiplanar reconstruction/reformation (MPR) method and the rendering method. In the MPR method, any desired cross-sectional plane can be displayed from the 3D data. In the rendering method, the 3D data are displayed to give the appearance of a 3D object projected onto a 2D plane. The volume rendering method is more suitable for 3D ultrasound data. There are two volume rendering methods: the translucent display method and the maximum intensity projection (MIP) method. The translucent display method employs the concept of opacity. It is possible to change the image characteristics by adjusting the opacity curve and the image quality parameters (transparency and threshold). In the rendering method, Doppler mode or the perspective projection method can be used in combination, improving and expanding the visualization capabilities in diagnostic applications. Global illumination has been realized by photon mapping technology. The position of the light source and the effects of indirect lighting are simulated, resulting in extremely realistic 3D display. In order to obtain high-quality 3D images, it is necessary to acquire the 3D ultrasound data under optimal conditions. In volume rendering, the threshold, transparency, and filter settings for image smoothing all affect the image quality. It is important to select the appropriate display method and to set the optimal imaging conditions to obtain the best possible image quality in clinical diagnosis.