Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 7 2 2022 09 26 82 85 katayoun katebi Department of Oral and Maxillofacial Medicine, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran. Ali Taghavi Zenouz Department of Oral and Maxillofacial Medicine, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran. Mohammad Ali Ghavimi Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran. 2021 05 29 2021 12 01 Methotrexate is an anti metabolite drug that is used for treating several autoimmune diseases in low doses. It has been reported that oral ulcers occur in 11-17% of patients receiving low doses of Methotrexate. The purpose of this article is to report the Meth- otrexate-induced oral ulcers and their effects on patient’s quality of life. The patient was a 69-year-old woman with a complaint of oral ulcers. She was taking alendronate, Methotrexate, and hydroxychloroquine for osteoporosis and rheumatoid arthritis dis- eases. The possibility of bisphosphonate-induced osteonecrosis was recognized due to necrotic ulcers with mandibular bone exposure in the first therapy session. Then, a new necrotizing ulcer on the hard palate appeared in the next session. Methotrexate consumption was discontinued and folic acid was initiated. The oral ulcers were fully recovered in three weeks. Methotrexate-induced mucositis should be considered in the differential diagnosis of patients with oral ulcers who receive low-dose Metho- trexate. https://crcp.tums.ac.ir/index.php/crcp/article/view/547