Neuroendocrine neoplasms arise in almost every organ of the body and are variably defined according to the site of origin. This Review focuses on neuroendocrine neoplasms of the digestive tract and pancreas. The 2010 WHO classification of tumors of the digestive system introduces grading and staging tools for neuroendocrine neoplasms. A carcinoid is now defined as a grade 1 or 2 neuroendocrine tumor and grade 3, small-cell or large-cell carcinomas are defined as neuroendocrine carcinoma. Epidemiological data show a worldwide increase in the prevalence and incidence of gastroentero-pancreatic neuroendocrine tumors in the past few decades, which is probably due to improved methods of detection of these tumors. The current diagnostic procedures and treatment options for neuroendocrine neoplasms are defined and summarized in the Review, although evidence-based data are lacking. Surgery remains the treatment mainstay and somatostatin analogues the basis for both diagnosis and therapy as the only 'theranostic' tool. Emerging compounds including chemotherapeutic agents, small molecules and biological therapies may provide new hope for patients.