Fluid and electrolyte balance is an important everyday practice on the intensive care unit. The different types of fluids are crystalloids that include Hartmann's solution, normal (isotonic) saline, dextrose, and colloids that include albumin, starch and gelatins. The disorders of sodium concentration are nearly always caused by excess free water (hyponatraemia) or free water loss (hypernatraemia). The potassium balance is affected by hypokalaemia and hyperkalaemia. The abnormalities in magnesium are caused by hypomagnesaemia and hypermagnesaemia. The abnormalities in phosphorous are caused by hypophosphataemia and hyperphosphataemia. The abnormalities in calcium are caused by hypocalcaemia and hypercalcaemia. Hypercalcaemia is not a common problem in intensive care. In 90% of cases, the underlying cause is hyper-parathyroidism or malignancy. Treatment is indicated when the hypercalcaemia is associated with adverse effects, or when the serum calcium is greater than 14 mg/dl (ionized calcium above 3.5 mmol/l).