The folic acid antagonists, aminopterin and then methotrexate, have been the primary systemically administered drugs for the treatment of severe psoriasis for 25 years. Methotrexate was finally approved by the FDA 5 years ago and was recently estimated to be used for approximately 25,000 psoriatic patients annually. With the small but chronic doses used for psoriasis, methotrexate has been relatively safe, except for a limited occurrence of significant hepatotoxicity. The good to excellent results obtained in most patients must, therefore, be weighted against the small risk of liver damage. Methotrexate has also been used with some effectiveness in several other dermatologic conditions, including mycosis fungoides, dermatomyositis, pityriasis rubra pilaris, and others, although they are not yet FDA-approved indications. The recent successful introduction of photochemotherapy (psoralen and ultraviolet light) for moderate and severely affected psoriatics will probably lead to a substantial decrease in the number of patients requiring methotrexate.