Purpose : to review current knowledge concerning the use of magnesium in anesthesiology, the role of hypomagnesemia and hypermagnesemia in perioperative period, analizing the cardiologic problems related to blood serum concentration changes of magnesium that can interesting in primis the anaesthesist in perioperative period. Methods: References were obtained from Pubmed (1995 to 2009). All categories of articles were selected, such as reviews, meta-analyses, abstracts, clinical trials etc). Principal findings: Magnesium is a bivalent ion, like calcium, the fourth most common cation in the body, and the second most common intracellular cation after potassium. Magnesium deficiency has been demonstrated in 7-11% of the hospitalized patients and it has been found to coexist with other electrolyte disorders, particulary hypokalaemia or hypophosphatemia and, to a less extent, hyponatraemia and hypocalcaemia, in more than 40% of patients. Hypomagnesemia needs to be detected and corrected to prevent increased morbidity and mortality. Historically, magnesium sulphate has been proposed as a general anaesthetic. Magnesium reduces the catecholamine release during the stressful manouvres like intubation. Magnesium has also anti-nociceptive effects in animal and human models of pain by blocking the N- methyl-D-aspartate receptor and the associated ion channels and thus preventing central sensitization caused by peripheral nociceptive stimulation. So for some authors it reduces the need for intraoperative anesthetics and relaxant drugs and reduces the amount of morphine for the treatment of pospoperative pain. The use of magnesium is extended not only to general anaesthesia but also in loco-regional anaesthesia. The role of magnesium has been extensively studied in cardiology especially during myocardial infarction, arrhythmia and cardiac surgery. Recent studies show the important of magnesium to prevent the postoperative neurocognitive impairment during carotid endoarterectomy and its utility in treatment of severe asthma. Conclusions Magnesium has many known indications. In peioperative period blood serum concentration changes of magnesium are frequent so anesthesiologists need to know the role of this important cation.