Maternal exposures to aminopterin and methotrexate have been associated with a pattern of malformation which includes prenatal-onset growth deficiency, severe lack of ossification of the calvarium, hypoplastic supraorbital ridges, small, low-set ears, micrognathia, and limb abnormalities. We report on a patient whose mother received methotrexate during the first trimester of pregnancy and who, in addition to the structural anomalies typical of maternal methotrexate exposure, has significant developmental delay. This is the third patient exposed to folic acid antagonists with mental retardation, providing further evidence that developmental delay is one feature of fetal aminopterin-methotrexate syndrome. Therefore, it is recommended that formal developmental testing be performed in all patients prenatally exposed to methotrexate.