Referred pain from disorders of the cervical spine can be perceived as headache. The mechanism is convergence between trigeminal afferents and afferents of the upper three cervical nerves in the trigeminocervical nucleus. Cervicogenic headache cannot be diagnosed on clinical grounds alone. The definitive criterion is complete relief of pain after controlled diagnostic blocks of cervical structures or their nerve supply. The most rigorously studied example of cervicogenic headache is third occipital headache.