An attempt has been made to provide the anatomical background necessary for the understanding of the complex problem of vomiting. This has been dealt with in two sections: (1) active vomiting; (2) passive regurgitation. In the first section, the vomiting centre and its afferent pathways have been described, together with the detail of three “sphincters” which are concerned; these are the gastro-oesophageal, the laryngeal and the nasopharyngeal. In the second section, the various possible mechanisms for preventing gastro-oesophageal reflux have been discussed and a conclusion drawn as to the actual mechanism responsible. The intrinsic musculature of the oesophagus initiates closure of the “sphincter”, and this is completed by the pressure difference between abdomen and oesophagus, which maintains apposition of the mucosal folds. When the normal mechanism is interfered with (e.g., in hiatus hernia), the action of the diaphragm may replace part of the normal mechanism.