Migraine (with and without aura) is characterised by a marked heterogeneity of clinical symptoms. A variety of pathophysiological models has been proposed and a multitude of prophylactic strategies recommended. It appears that prophylaxis is still problematic, despite considerable progress in acute treatment. Most substances used for the former purpose either have substantial side effects or a wide range of contraindications. Magnesium (Mg) seems to play a significant role in the pathogenesis of migraine. A few clinical trials have produced preliminary evidence of therapeutic efficacy. There is a reasonable amount of empirical evidence, and further research is warranted considering its low cost and favourable side effects profile. An attempt at prophylaxis in mild to mid-severe migraine with a daily dose of 600 mg (about 50 mEq) Mg seems to be justified.