Patients with primary headache syndromes often describe a pain distribution, that does not respect the trigeminal innervation of the head. In addition to pain in frontal areas, innervated by the first (ophthalmic) division of the trigeminal nerve, the pain often occurs in occipital parts of the head, innervated by the greater occipital nerve, a branch of the C2 spinal nerve root. Anatomical and neurophysiological studies in animals suggest a convergence of cervical and trigeminal input in the trigeminal nucleus caudalis. Modulation of this pathway has been discussed to be of potential benefit in headache disorders. We investigated in an open pilot study the effect of bilateral block of the greater occipital nerve with 50 mg prilocaine and 4 mg dexamethasone in patients with chronic tension type headache. From 15 patients, only one patient described a headache relief after initial exacerbation of headache for 2 days. Headache intensity was unchanged in 11 patients. In further three patients, the headache worsened in the first hours or days after injection. No serious adverse events were observed. One patient showed a bradycardia (36/min) after the first injection during palpation of the muscles of the neck. Three patients suffered pain on the injection site for a few days. Our results indicate that block of the greater occipital nerve is not effective in the treatment of chronic tension type headache. If at all, rather a 'pro-nociceptive' effect was observed.