Many teeth have been mistakenly extracted or endodontically treated because of an incorrect diagnosis of orofacial pain, including toothache. A case of persistent toothache originating from a malignant lymphoma of the left maxillary sinus is presented. Root canal therapy and extraction of the upper left quadrant teeth from the canine to the second molar did not resolve the chief complaint. The patient was referred to a neurologist and received a diagnosis of a malignant lymphoma, a rare lesion of the maxillary sinus. This case stresses the importance of considering malignant neoplasm of the maxillary sinus as a potential etiologic factor in the differential diagnosis of orofacial pain.