Isotretinoin, an analog of vitamin A, belongs to the group termed “retinoids” that includes the well-known developmental toxicants etretinate, tretinoin, and acitretin. Isotretinoin is a potent developmental toxicant, including teratogenicity, in every animal species tested. Isotretinoin is also a potent teratogen in humans, and it affects most classes of developmental toxicity as well. One group of experts considers the teratogenic risk of the drug to be high. Characteristic features of the syndrome include central nervous system malformations, microtia/anotia, micrognathia, cardiac and great vessel defects, thymic abnormalities, and eye malformations. Functional deficits of several forms have been associated with malformations and death in isotre-tinoin-induced developmental toxicity. Several central nervous system malformations that may have been the cause of, and are associated with, functional impairment were described in the syndrome in high incidence, including hydrocephalus, cortical and cerebellar defects, and spina bifida, to name a few.