Physiologically, magnesium plays an essential role in bone formation, neuromuscular stability and muscle contraction, and the consequences of its altered homeostasis may be serious. Magnesium deficiency and hypomagnesemia are common and under-recognized problems, which can cause a variety of symptoms and can also affect the other cations metabolism. In this review causes, clinical picture and management of hypomagnesemia and magnesium deficiency are discussed.