The pathogenetic mechanism of tension headache (TH) is still unknown. The role of pericranial muscle tension in TH is also enigmatic. To evaluate this factor in chronic TH, pericranial muscles were paralysed in 6 chronic TH patients, using botulinum toxin. All patients fulfilled the IHS criteria of chronic TH associated with involvement of the pericranial muscles, but not the current criteria for cervicogenic headache. The patients were followed-up regularly with evaluation of the paralysis, changes in pain intensity, and pressure pain threshold measurements. We primarily only injected the temporal muscle on the one side, using the other side as a control. Contralateral muscles were in some cases injected at a later stage. In our study, we did not find any significant reduction in pain intensity, as measured by the visual analogue scale, nor any changes in pressure pain threshold, as measured by an algometer. On the basis of our observations, we conclude that muscle tension in these muscles possibly plays a minor role in the genesis of chronic TH. In our study, however, we have only treated a limited number of patients, and only one pericranial muscle has been injected systematically. Further studies of various neck/posterior head muscles ought to be performed in order to further evaluate a possible effect of tension in the pericranial musculature in producing this type of pain.