Neuroendocrine tumours of the digestive tract are rare neoplasms deriving from the neuroendocrine cells spread along the digestive tract from the oesophagus to the rectum. This books aims to summarize the current knowledge about the origin and hormones of neuroendocrine cells in the digestive tract and the current staging- and grading systems for neuroendocrine tumours. Data on the incidence of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have so far only been obtained retrospectively and are based on inhomogeneous material. So the research part of this book presents a prospective study collecting all newly diagnosed GEP-NETs in Austria during one year. Using the WHO 2000- classification, the TNM staging and Ki67-grading, and the standard diagnostic procedure proposed by the European Neuroendocrine Tumor Society (ENETS), GEP-NETs from 285 patients were recorded. Additionally the practice of diagnosis and treatment in Austria is addressed and describes "unmasked" clinical symptoms, methods of diagnosis, treatment, and short-term follow-up of neuroendocrine tumors of the digestive tract diagnosed during one year in Austria.