'Sinus headache' is a term used by many patients and primary-care physicians and, contrary to popular belief, sinus headaches are uncommon. Headaches that are due to sinusitis are confined to a minority of patients who have acute frontal sinusitis or sphenoiditis. The International Headache Society classification is robust in qualifying the term sinus headache and says that "chronic sinusitis is not validated as a cause of headache and facial pain unless relapsing into an acute stage". The vast majority of people who present with a symmetrical frontal or temporal headache, sometimes with an occipital component, have tension-type headache. Unilateral, episodic headaches are often vascular in origin. The idea that sinusitis can trigger migraine is misplaced, as the whole symptom complex is vascular and coexisting nasal congestion is due to vasodilation of the nasal mucosa that is sometimes part of the vascular event. The use of nasal endoscopy and imaging of the paranasal sinuses have advanced our appreciation that these patients are suffering from a vascular event. When these patients are asked to attend a clinic when they are symptomatic, the vast majority are found not to have a sinus infection. Sinusitis rarely causes headache, let alone facial pain, except when there is an acute bacterial infection when the sinus in question cannot drain, and it is usually unilateral due to increased pressure and inflammation caused by pus trapped within the sinus cavity. These patients usually have a history of a viral upper respiratory infection immediately before this and they have pyrexia with unilateral nasal obstruction. The vast majority of patients with acute sinusitis respond to antibiotics. Recurrent bacterial sinusitis is rare and anyone with more than two episodes of genuine bacterial sinusitis in 1 year should be investigated for evidence of poor immunity. Patients with chronic bacterial sinusitis rarely have any pain unless the sinus ostia are blocked and their symptoms are then the same as in acute sinusitis. Within the medical literature, there are texts that report that sphenoid sinusitis can cause headaches and, as with other acute sinus infections, intracranial or ophthalmolgical complications can occur. First, acute sphenoid sinusitis is rare and second, most of these patients respond to antibiotics. Batotrauma can cause short-lived pain in the sinus involved but there is always a clear history associated with diving or flying and, as the pressure within the sinus equalizes, the pain resolves within a few hours. Headaches are rarely due to sinusitis.