Several studies have reported an involvement of the stomatognathic system in the course of fibromyalgia (FM) similar to that which characterizes temporomandibular disorders (TMD). The aim of this study was to investigate and compare the clinical features of stomatognathic dysfunction in patients with FM and TMD. Ninety-three FM patients underwent an assessment according to the RDC/TMD guidelines. Prevalence of the different RDC/TMD diagnoses and some clinical parameters of FM patients were compared with those of 181 patients affected by TMD. Seventy-four (79.6%) FM patients presented at least one RDC/TMD diagnosis and showed lower mean maximum voluntary and passive mouth opening values than TMD patients. Moreover, 34 FM patients presented with trigger and/or tender points. Results of the present study confirm the high rate of involvement of the stomatognathic system in the course of FM and support the need for a careful multidisciplinary approach to patients with TMD, including the rheumatologist.