Magnesium has an established role in obstetrics and an evolving role in other clinical areas, in particular cardiology. Many of the effects involving magnesium are still a matter of controversy. Over the next decade, it is likely that improvements in the measurement of magnesium, a clearer understanding of the mechanisms of its actions and further results of clinical studies will help to elucidate its role, both in terms of treating deficiency and as a pharmacological agent.