The long‐term prognosis of craniopagus, a congenital abnormality of monozygotic twinning, is strictly correlated to the type of shared cerebral structures. Hence, the purpose of prenatal diagnosis is not only to detect this malformation, but also to identify the fused cerebral structures. The authors report a prenatal diagnosis of a craniopagus during the second trimester of pregnancy. Comparison of ultrasound data with the pathological findings underlines that ultrasound is of great value in detecting malformations, but it is not alone sufficient to identify the types of conjoined cerebral structures.