The endocrine tumors of the gut and pancreas tract are a group of neoplasms composed of cells with a neuroendocrine phenotype. Well-differentiated tumors, well-differentiated carcinomas and poorly differentiated carcinomas are the major categories identified. According to their localization (stomach, duodenum-jejunum, ileum, appendix and colorectum), they display distinct phenotypes, regarding their pathology, immunohistochemistry and hormonal syndromes. Their clinical behavior spans from benign, uncertain malignant potential, low-grade malignant to high-grade malignant. Currently, extensive work is performed to unravel the genetic background.