Although pleomorphic lipoma may contain a small number of atypical cells and resembles an atypical lipomatous tumor histologically, it is a tumor characterized by a clinically benign course. Pleomorphic lipoma typically arises in the posterior cervical region, shoulders, and back, with relatively few reported cases of the tumor in the oralmaxillofacial region. We report on a 60-year-old man with a pleomorphic lipoma that developed from the neck to the submandibular region and was left untreated for more than 40 years because the patient was asymptomatic. The tumor was removed together with its fibrous capsule. Twenty months after surgery, the patient remains recurrence-free and has a good clinical course. Among 39 reports of this tumor in Japan that we searched this time, only one case similat to ours was reported, but reports of pleomorphic lipoma arising in the cervical region are rare in Japan. : pleomorphic lipoma (多形性脂肪腫) ，floret cell (花冠状細胞) ，submandibular region (顎下部) 1) 名古屋掖済会病院歯科口腔外科 (主任：足立守安部長) 2) 愛知学院大学歯学部顎口腔外科学講座 (主任：栗田賢一教授) 3) 静岡県立総合病院歯科口腔外科 (主任：林 尚徳主任医長) 1)

＊ ：We report a case of multiple osseous dysplasia with simple bone cysts in the jaw bones of both sides of the maxillary molar part, right maxillary front tooth part and part from the right lower second molar to the left lower second molar part, with long-term follow-up. The patient was a 61-year-old woman. Although she had no subjective symptoms, the patient underwent surgery because the simple bone cysts tended to enlarge during the 18-year follow-up period. The surgical treatment consisted of cystic fluid evacuation, filling the cavity with blood, and primary closure. After repeated surgery, the simple bone cysts of the patient eventually filled with normal bone tissue. We therefore consider this treatment to be effective. ：osseous dysplasia（骨性異形成症） ，simple bone cyst（単純性骨囊胞） ，long term observation（長期経過観察）