A 66-year-old osteoporotic woman suffered from long-term mental paresthesia (numbness), facial swelling, and a nonhealing extraction site. Fulfilling the three clinical diagnostic criteria for bisphosphonate-related osteonecrosis of the jaw (BRONJ; exposed bone for at least 8 weeks, current bisphosphonate [risedronate] treatment, and no history of head and neck radiation therapy), she was diagnosed and treated accordingly. Nevertheless, a later histopathologic examination revealed malignant lymphoproliferative infiltration of large and intermediate cells. Based on immunostaining and positron-emission tomography, she was diagnosed as having primary diffuse large B-cell lymphoma. This case demonstrates the limitation of the current diagnostic method of BRONJ. Thus, the clinician should be particularly cautious and aware of the differential diagnosis, including malignancy, especially when lesions are accompanied by (mental nerve) neuropathy and long-standing swelling/expansion, and even when plain radiography is not a contributing factor. Keywords: bone, numb chin syndrome, paresthesia, trigeminal neuropathy, wound healing