In addition to vascular and supraspinal influences, contraction of craniofacial muscles or central sensitization processes following continuous nociceptive input of craniofacial muscles may play an important role in the pathogenesis of tension-type headache. Chemodenervation induced by botulinum toxin injection is successfully used to decrease muscle tension. If muscle tension is important in this type of headache, then botulinum toxin could be helpful in its treatment. We conducted a randomized, placebo-controlled study to examine the effect of 20 U botulinum toxin injected into frontal and temporal muscles in patients with chronic tension-type headache. During a baseline of 4 weeks and a posttreatment period of 8 weeks, the effect was evaluated with daily records and the West Haven-Yale Multidimensional Pain Inventory. Some improvement in affective variables were demonstrated in the botulinum group, but important outcome variables, such as pain intensity, the number of pain-free days, and consumption of analgesics, were not statistically different between the groups. Reasons for these moderate effects may include the injection sites, dose of botulinum toxin, and duration of treatment.