This study compared myofascial pain of the masticatory muscles to fibromyalgia. Study data show that, in both myofascial pain and fibromyalgia patients, facial pain intensity and its daily pattern and effect on quality of life are very similar. This indicated that fibromyalgia should be included in the differential diagnosis for myofascial pain of the masticatory muscles. However, with the higher prevalence of neurologic and gastrointestinal symptoms, and the stronger words used to describe the affective dimension of pain, it is apparent that fibromyalgia may be a more debilitating condition than myofascial pain of the masticatory muscles. Since the intensity of facial pain was strongly and significantly correlated to the body-pain index in fibromyalgia but not in myofascial pain patients, it can be concluded that facial pain may be part of the clinical manifestations of fibromyalgia, but it is unlikely to be related to body pain in myofascial pain patients. On the other hand, while body pain is episodic in most myofascial pain patients, it is constant and more severe in the majority of fibromyalgia patients. This difference in the pain patterns suggests that body pain in fibromyalgia and myofascial pain could have different etiologies. The lack of correlation between the intensity of pain and the length of time since onset also supports the concept that myofascial pain of the masticatory muscles and fibromyalgia are unlikely to be progressive disorders.