Over the past 40 years, human magnesium deficiency has become recognized as a world-wide clinical problem. In 1926, Leroy (1), demonstrated the absolute need of magnesium for growth and life in mice, and the need for magnesium in plants was demonstrated in 1860. Although clinical deficiency was first reported in 1934, it was not until the 1950s that interest in clinical magnesium deficiency developed rapidly. Before the 1950s, textbooks of medicine, pediatrics and biochemistry did not mention magnesium disturbances. In this paper I shall emphasize the recognition and treatment of magnesium deficiency by giving details of the setting, i.e. illnesses, the multifaceted manifestations, the laboratory findings and safe protocols for treatment.