Three-dimensional endorectal sonography with a specially developed system is able to produce an image of the entire pelvic floor including the sphincter muscles and the rectal wall even in small children. This special system is based on conventional endorectal ultrasound and allows recording of a controlled withdrawal of the axially rotating transducer, creating an image sequence resembling that of a spiral CT-scan; this sequence is digitized off-line and evaluated in a three-dimensional form by a workstation computer. This evaluation has several advantages compared with conventional examination, for example, the complete recording of organs with the possibility of volumetry, construction of arbitrary sections, volume-rendering procedures and the interactive segmentation of organ borders and their three-dimensional visualization. Based on images from this 3D endorectal sonography, the normal anatomy of the pelvic floor that is visible using ultrasound is described, followed by some pathological findings concerning continence surgery. Finally we discuss the advantages and restrictions compared to other examination procedures and the possibilities of technical development.