Objectives: To compare the long-term effectiveness of a prefabricated occlusal appliance with a stabilization appliance in myofascial pain patients. Methods: Sixty-five patients with the diagnosis myofascial pain at two centres for Stomatognathic Physiology in Sweden and Finland were included in a randomized controlled trial. Patients were randomly assigned to a prefabricated appliance (R-group, 27 women, 5 men, mean age 38 years) or a stabilization group (S-group, 31 women 2 men, mean age 37 years). General practitioners performed the treatment. History and clinical examination was performed according to RDC/TMD. At the 6 months- and 1 year follow-up the treatment outcome regarding pain according to the visual analogue scale and overall rating of pain according to the verbal scale was evaluated. Results: At baseline there were no differences between the groups regarding frequency of myofascial pain, number of years suffering from the pain, worst or mean pain during the last six months. At the 12-months follow-up 30% and 50% pain relief in the R- and S-groups were reported in 24 and 21 patients and 23 and 17 patients respectively. According to a verbal scale 26 and 21 patients in the two groups reported themselves to be better, much better or symptom-free. All calculations were done per protocol. An increased open bite was registered in one patient. Conclusions: In a long-term perspective both appliances seemed to have an equal effectiveness in the treatment of patients suffering from myofascial pain. The prefabricated appliance, Relax, can be recommended as a long-term treatment modality when used night time only. Frontal open bite should be regarded as a contraindication.