A case of a patient with a malignant schwannoma, who was originally diagnosed as having internal derangement of the temporomandibular joint (TMJ), is presented. This is only the second reported case of this tumor with TMJ symptoms. The importance of obtaining adequate TMJ radiographs as part of the initial data collection process is stressed. Computed tomography (CT) and magnetic resonance imaging (MRI) scans are suggested if the patient has any of the ominous signs or symptoms mentioned in the text. When a patient is initially diagnosed with TMJ disease, failure to respond to appropriate therapy should alert the clinician that the initial diagnosis may be incorrect.