The perioperative fluid management of neurosurgical patients presents special challenges for the clinician. The traditional approach to fluid management of patients, with intracranial mass lesions or brain swelling, often includes volume restriction. Though comfortable for the surgeon, the severe volume restriction leads to some major problems for the anaesthesiologist, e.g. hypovolaemia, hypoxaemia, electrolyte and acid-base abnormalities. The modern approach to management requires that patients have reasonable circulating volumes to avoid hypotension and to tolerate the changes induced by anaesthesia (peripheral vasodilatation and myocardial depression), surgery and other associated causes. Preoperative fluid management should be designed to decrease brain water content, thereby reducing intracranial pressure (ICP) and providing adequate brain relaxation, perioperative maintenance crystalloids are usually administered at a rate of 1 to 1.5 ml/kg/hr, preferred crystalloid being normal saline. Intraoperative fluids should be given at a rate that is sufficient to replace the urinary output and insensible losses (e.g. skin and lungs). A detailed description of intravenous fluids to be given for different neurosurgical procedures is given in this chapter.