Migraine is frequently associated with menstruation in female migraineurs, and consequently it is commonly referred to as menstrually associated migraine. The trigger thought to be partially responsible for menstrually associated migraine is a significant drop in circulating estrogen that is noted during 2-3 days prior to onset of menses. It is estimated that approximately 50% of women have an increased risk of experiencing migraine during the premenstrual phase of decreasing estrogen levels. Understanding the biological basis of migraine associated with menses will facilitate an accurate diagnosis and help patients recognize time susceptible to migraine exacerbations. This paper will review the biological bases for the hormonal changes that occur during the menstrual cycle and review the prevalence and burden of menstrual migraine among female headache sufferers.