Our understanding of the sonographic anatomy of the pelvic floor has developed following technical improvements in image quality, and the ability to break free of the restrictions imposed by fixed-plane imaging. Threedimensional (3D) imaging provides representation of structures in their true anatomical plane, and has allowed direct comparisons to be made with magnetic resonance imaging (MRI). MRI gives hard anatomical detail with striated muscle clearly defined. Using information from a variety of sources such as surgery and cadaveric dissection, but particularly 3D endosonography, to colocate endocoil MRI images, it has been possible to work out the exact anatomical detail of the sphincter. Once the sonographic appearances have been established in this way, greater reliance can be placed on their interpretation. This methodology has been key in developing the sonographic investigation of the pelvic floor.