Proventricular dilatation syndrome is a disease syndrome of psittacine birds that is most often characterized by a wasting bird suffering from malnutrition and/or one suffering from a nervous disorder. It affects most notably the central nervous system and the nerves of the gastrointestinal system. Specifically it causes an obliteration of the nervous tissue by inflammatory cells. Its clinical signs are caused by damage to the nerve supply of a speci'fic organ, most often the proventriculus.