Magnesium is a participant in many metabolic processes. Its concentration in the body is regulated by the kidneys. Normal diet contains sufficient amounts of magnesium, and significant magnesium deficiency in healthy individuals with normal nutritional status is rare.Magnesium deficiency should be suspected if the patient has compatible symptoms or clinical findings or an underlying factor predisposing to such deficiency.The most common symptoms and findings in hypomagnesaemia are neurological or psychiatric. Only 1% of total body magnesium is in the plasma, which impedes the evaluation of magnesium deficiency. Normal plasma magnesium concentration does not rule out deficiency, but low plasma magnesium concentration almost always signifies true deficiency.