Sinus headache is commonly diagnosed, and patients with headache often cite sinus pain and pressure as a cause of their headaches. A high frequency of diagnosis of sinus headache, which specialists consider to be relatively rare, among patients meeting International Headache Society (IHS) diagnostic criteria for migraine raises the possibility that migraine and perhaps other headache types are sometimes mistaken for sinus headache. This article considers clinical, epidemiologic, and pathophysiologic relationships between sinus headache and migraine and discusses the implications for clinical management of headache. Both historic and new data show that nasal symptoms frequently accompany migraine, although these symptoms are not part of the IHS diagnostic criteria for migraine. Parasympathetic activation, as well as the hypothesized mechanism of neurogenic or immunogenic switching (i.e., crossover interactions of neurogenic and immunogenic inflammation), may account for both the frequent occurrence of nasal symptoms in migraine and the possibility that sinus inflammation can sometimes act as a migraine trigger. Considered in aggregate, the data show that the occurrence of nasal symptoms associated with a headache should neither trigger a diagnosis of sinus disease nor exclude a diagnosis of migraine. It should, in fact, prompt diagnostic consideration of both conditions.