Although the possibility of a comorbidity between migraine and hypertension has long been suspected, the epidemiologic evidence is controversial, with studies demonstrating positive, negative or no correlation between the two diseases. A unifying view that takes into account the most recent evidence suggests that there might be a different effect of diastolic and systolic pressure, with the former having a positive and the latter a negative correlation with migraine. In this paper, the methodologic and clinical reasons for the discrepancies in epidemiologic studies are discussed, together with the possible biological mechanisms that might account for the migraine-hypertension correlation. One such mechanisms may be the renin angiotensin system, which is certainly involved in hypertension and has activities in the CNS that may be relevant for migraine pathogenesis. Despite the uncertainty still present in this field, the control of hypertension in migraine patients is an important factor for the success of migraine treatment and to lower cerebrovascular risk.