Aminopterin is a folic acid antagonist occasionally used as an abortifacient (a drug to induce an abortion) in early pregnancy; methotrexate, the methyl derivative of aminopterin and also an abortifacient, is used to treat rheumatoid arthritis and psoriasis. Offspring of mothers treated with either drug early in pregnancy may show a complex of craniofacial, growth, and limb abnormalities. An apparent critical period for adverse effects occurs at 6-8 weeks post-conception. Fetal or early postnatal death may occur. In survivors, the most apparent feature are facial dysmorphologies, which result in a characteristic appearance. Surprisingly, given frequent microcephaly, intelligence and motor behavior are largely unaffected. The disorder is rare and accurate incidence figures are not available.