Objective. To compare the short- and long-term effectiveness of a prefabricated occlusal appliance with that of a stabilization appliance when treating headache in patients with myofascial pain. Material and methods. Sixty-six patients, 94% of whom suffered concomitantly from headache, at two centres for Stomatognathic Physiology in Sweden and Finland were included in a randomized controlled trial. History questionnaires and clinical examination according to the Research Diagnostic Criteria for Temporomandibular Disorders were used at baseline and at 10-week and 6- and 12-month follow-ups. Patients were randomly assigned to either a prefabricated (R) or a stabilization appliance (S) group. Results. There were significant decreases in the frequency and intensity of headache in both groups at all follow-ups, without statistically significant differences between groups. At baseline, 23 patients in both groups reported recurrent-continuous headache and, at 12 months, seven in the R group and four in the S group. The mean intensity (numeric rating scale) of headache prior to treatment decreased significantly at 12 months from 5.3 to 2.1 in the R group and from 6.1 to 2.9 in the S group. At the 12-month follow-up, 56% of patients in the R group reported a 30% reduction in intensity of headache and 50% a 50% reduction. In the S group, corresponding values were 39% and 36%, respectively. Non-specific physical symptoms were significantly associated with frequency of headache at baseline and at 6 months, and with depression at 6 and 12 months. Conclusion. The effectiveness of the prefabricated appliance seems to be similar to that of the stabilization appliance in the treatment of headache in patients with myofascial pain in both the short and long term. [ABSTRACT FROM AUTHOR]