The isotretinoin, a 13-cis-retinoic acid, has revolutionized the management of severe treatment-resistant acne and it has been widely used for a range of dermatological conditions, in 90% of the time in young women between 13 and 45 years of age. This agent has severe teratogenic effects, as serious craniofacial, cardiovascular, thymic and central nervous system malformations. The baseline population risk of malformations is 3-5%, but it increases to almost 30% in women exposed to isotretinoin during the first trimester of pregnancy. Generally, patients in treatment with isotretinoin avoid eventual pregnancy during assumption and, after its stopping, fertility and foetal development are normal once circulating isotretinoin levels return to normal. There are no known deleterious effects on male fertility and on long-term teratogenic effect of isotretinoin. In this report, we suppose the possibility to develop a foetal malformations after a long-term wash out from isotretinoin therapy. A 32 year-old healthy nullipara pregnant woman, with an uneventful past gynaecological history, was admitted in Hospital, with a severe depressive syndrome in a 18 weeks malformed pregnancy for thoraco-omphalopagus conjoined twins. She only assumed isotretinoin, at dose of 1 mg/kg a day, for a severe and scarring acne for 7 months. After 3 months of pharmacological wash out, patient become pregnant and manifested this severe malformation. Woman interrupted gestation, by labour induction.