The problem that our research addresses is the lack of a comprehensive, universally useful system for navigating 3D images ofanatomical structures. In this paper we discuss the organization of anatomical information in a navigational ontology, a knowledge representation formalism that supports intelligent browsing of 3D anatomical images. For the purposes ofthis project, 'intelligent' means that the computer system behaves as if it had accurate knowledge of human anatomy consistent with that of a trained anatomist (though not necessarily as complete). To give a simple example, if the user asks to see the component structures of the urinary system, the system will return to the user either a list of structures and/or a model of them, just as an anatomy instructor might do. The Vesalius Anatomy Browser provides an interface for navigating 3D anatomical images in which anatomical images are linked to a hierarchical representation of conceptual information that corresponds directly to the images displayed on the screen. The association of the concepts with images makes possible simultaneous visual exploration of anatomical information via word and image