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Methotrexate is an antimetabolite analog to folic acid that competitively inhibits the enzyme dihydrofolate reductase and thymidylate synthetase, essential for the synthesis of DNA and RNA. It is widely used in dermatology and its adverse effects on the skin and mucous membranes are varied, including mild and severe reactions. The appearance of erosions and skin ulcers as a manifestation of methotrexate cytotoxicity are quite infrequent. These would represent an early cutaneous sign of pancytopenia due to marrow toxicity secondary to this drug. In most of the cases there are cutaneous diseases prior to ulceration, mainly psoriasis. In the absence of underlying dermatitis, the presence of ulcerations is very rare. We present eight cases of patients with cutaneous signs of methotrexate poisoning, with and without previous dermatoses. Most of them associated mucositis and bone marrow involvement. Treatment guidelines are recommended.