Gastrointestinal neuroendocrine tumours are classified as functioning or non-functioning according to the presence or absence of a clinically evident hypersecretion syndrome. In foregut tumours the presence of autonomous hormone secretion and the respective hypersecretion syndrome indicate functionality. Abdominal ultrasound (US), computed tomography (CT), magnetic resonance tomography (MRT) and somatostatin receptor scintigraphy (SRS) are used for localisation of the primary tumour and metastasis. Invasive procedures such as endoscopic US, intraoperative US or intraoperative duodenal transillumination are useful to localise small (< 1 cm) tumours. For localised tumours surgery is the first line treatment. In metastatic disease symptomatic therapy, biotherapy and chemotherapy are available. Cytoreductive therapy such as embolisation, chemoembolisation, thermo- or cryotherapy, or radio-receptor therapy are additional options. The first symptom of most neuroendocrine midgut tumours is abdominal pain. An increased chromogranin-A plasma concentration or 5-hydroxyindoleacetic acid 24-h urinary excretion indicates the neuroendocrine origin of the tumour or the possibility of a carcinoid syndrome, respectively. Surgical therapy prolongs survival but is rarely curative. Biotherapy is effective as symptomatic therapy. However, its cytoreductive potency is low. Chemotherapy is less effective in midgut tumours compared to foregut tumours. Cytoreductive strategies (chemoembolisation, thermo- or cryotherapy, cytoreductive surgery) and radio-receptor therapy may offer new therapeutic options. However, their definitive value has yet to be defined.