A subset of gastrointestinal neuroendocrine tumours [carcinoids and pancreatic endocrine tumours] show aggressive growth. Early identification of this subset is essential for management; however clinical, laboratory and histologic features frequently fail to achieve this. Currently, there is an increased understanding of the molecular pathogenesis/changes in neuroendocrine tumours and this may identify important prognostic factors and possibly, new treatments. Recent findings and progress in this area are briefly reviewed in this article.