We report on a 54-year-old Japanese man who was referred to the Department of Oral and Maxillofacial Surgery with the symptoms of erosive stomatitis and ulcer on the upper and lower gingivae and bilateral buccal mucosae. Laboratory tests showed elevated levels of anti-desmoglein 1 and 3 antibodies. Although steroid therapy was advised under a diagnosis of pemphigus vulgaris to prevent exacerbation, only a topical steroid was applied to the oral mucosae because of the patient’s nonadherence to his medication. One month after the initial visit, dermal vesicles and erosion were reported on the entire body. An underlying neoplasm was not identified on whole body positron emission tomography imaging or gastrointestinal endoscopic examination. Pemphigus vulgaris was diagnosed on the basis of clinical, pathological, and laboratory findings. Medication therapy with prednisolone (50 mg/day) and topical steroid ointment were performed under hospitalization. The erosions were successfully treated with the steroid therapy. However, 14 days after receiving treatment during hospitalization, the patient died of pulmonary hemorrhage approximately 2 months after the initial visit.