Fasting, anaesthesia and surgery affect the body's physiological capacity not only to control its external fluid and electrolyte balance but also the internal balance between the various body fluid compartments. Conversely, abnormalities of fluid and electrolyte balance may adversely affect organ function and surgical outcome. Perioperative fluid therapy has a direct bearing on outcome, and prescriptions should be tailored to the needs of the patient. The goal of fluid therapy in the elective setting is to maintain the effective circulatory volume while avoiding interstitial fluid overload whenever possible. Weight gain in elective surgical patients should be minimized in an attempt to achieve a ‘zero fluid balance status’. On the other hand, these patients should arrive in the anaesthetic room in a state of normal fluid and electrolyte balance so as to avoid the need to resuscitate fluid-depleted patients in the anaesthetic room or after the induction of anaesthesia. Optimal fluid delivery should be part of an overall care package that involves minimization of the period of preoperative fasting, preoperative carbohydrate loading, thoracic epidural analgesia, avoidance of nasogastric tubes, early mobilization, and early return to oral feeding, as exemplified by the enhanced recovery after surgery programme.