This is the protocol for a review and there is no abstract. The objectives are as follows: The general objectives of this review are: To determine if muscle relaxants are effective in the prophylactic treatment of tension-type headache (TTH). To describe the safety of using muscle relaxants in the prophylactic treatment of TTH. More specific objectives are to: To determine if treatment with muscle relaxants reduces the number of days with headache. To determine if treatment with muscle relaxants results in some proportion of patients becoming free of headache. To determine if treatment with muscle relaxants decreases headache duration. To determine if treatment with muscle relaxants decreases headache intensity. To describe the frequency of adverse effects associated with muscle relaxants used for the prophylactic treatment of TTH.