Secondary headaches account for about 10% of headaches and require meticulous diagnosis because of their life-threatening potential. The secondary headaches include a diverse and fascinating array of etiologies which can mimic primary headache disorders ranging from the rare to the mundane and from the well established to the highly controversial. This issue of Neurologic Clinics is devoted entirely to secondary headaches with topics that include: Headaches due to nasal and paranasal sinus disease; Headaches due to vascular disorders; Headaches and brain tumors; Low cerebrospinal fluid pressure syndromes; Painful ophthalmologic disorders and eye pain; Idiopathic intracranial hypertension (pseudotumor cerebri); Cough, exertional, and sex headaches; The neck and headaches; Drug-induced headaches; Trigeminal neuralgia and glossopharyngeal neuralgia; Headaches and vasculitis; Tonsilar ectopia and headaches; Post-traumatic headaches; Metabolic headaches; Temporomandibular joint disorders, bruxism, and headaches.