An understanding of the anatomy of the anorectum is essential to the understanding of the disease processes that occur in this area. Physiology of the anorectal region is very complex, and the maintenance of anal continence depends upon a highly integrated series of complicated events upon which there is not uniform agreement. A brief description is made of the various modes of investigation available to establish a diagnosis, provide an objective assessment of function, or identify the anatomic site of a lesion. This is followed by a list of disorders that have been studied in an effort to better determine their pathogenesis.