A comprehensive and critical review of the evidence relating magnesium (Mg) deficiency to alcohol consumption reveals several important types of interactions. First, alcohol acts acutely as a Mg diuretic, causing a prompt, vigorous increase in the urinary excretion of this metal along with that of certain other electrolytes. Second, with chronic intake of alcohol and development of alcoholism, the body stores of Mg become depleted. During the late stages of alcoholism, the urinary excretion of Mg may become diminished as a physiological response to reduced intake and reduction of body stores. A number of aspects of the clinical syndrome of alcoholism contribute to and intensify that already existing reduction in body Mg stores. Third, a number of manifestations of alcoholism are believed due to effects of Mg deficiency, and some therapeutic benefit has been suggested from treatment of alcoholic patients with Mg. Finally, relatively little attention has been paid to the possible value of Mg administration as a preventive measure to forestall or minimize the deleterious effects of chronic use of alcohol or to prevent the development of cancer than can occur in this setting.