Methotrexate (MTX) remains one of the most frequently used anti-metabolite agents in dermatology. MTX is an analog of folate that competitively and irreversibly inhibits dihydrofolate reductase. Oral mucositis is a common side effect of chemotherapy drugs and is characterized by erythema, pain, poor oral intake, pseudomembranous destruction, open ulceration and hemorrhage of the oral mucosa. In this paper, we report a 32-year-old female with a case of mucositis due to MTX intoxication that resulted from an overdose for rheumatoid arthritis. The patient had abdominal pain, vomiting, and nausea. During follow-up, the patient's white blood cell count was found to be 0.9 x 10(9)/L (4-10 x 10(9)/L). The patient developed fever exceeding 40 degrees C. The patient was consulted to the hematology service. They suggested using granulocyte colony-stimulating factor for febrile neutropenia. On the fifth day of treatment, the white blood cell count reached 5.3 x 10(9)/L and the patient's fever and mucositis started to resolve. Here, we presented a case of hemorrhagic mucositis and febrile neutropenia resulted from high-dose MTX that responded very well to granulocyte colony-stimulating factor treatment and we reviewed the literature.