Abstract
Methotrexate is one of the most used drugs in the treatment of psoriasis with indication of systemic therapy. Cutaneous and mucous side effects are described by pharmacological characteristics of the drug itself or due to overdose. We report the case of a patient with ulcerations in oral mucosa and psoriatic plaques after incorrect use of Methotrexate. Prescribed in a weekly dose, it was used continuously for 10 days and without simultaneous intake of folic acid. It is important to ensure correct comprehension of the prescription.