Unilateral cranial autonomic symptoms (UAs) such as lacrimation, conjunctival injection, eyelid oedema and nasal congestion, which are the hallmark of trigeminal autonomic cephalgias, may also occur in an as yet undetermined proportion of migraine patients. We studied 177 consecutive migraineurs to assess the frequency of UAs and the clinical characteristics of such patients. UAs were reported by 81 patients (45.8%), ocular symptoms alone or in combination with nasal symptoms being the most frequent. The headache was more severe (P<0.0002) and more strictly unilateral (P<0.0004) in patients who reported UAs than in those without. Thus, the presence of UAs suggests an activation of the trigeminal-autonomic reflex, probably related to an over-activation of the trigeminal afferent arm. These findings could have therapeutic implications, given the potential large-scale recruitment of peripheral neurovascular 5-HT1B/1D receptors (the target of acute migraine treatment) in such patients.