Double anueploidy, involving both trisomy 18 and Klinefelter syndrome at the same time, is a rare event, in which the features of Edwards syndrome dominate the clinical picture. We describe a patient, who was diagnosed in the 8th gestational week with a seemingly normal intrauterine pregnancy with “chorionic bump”. In the 12th week the following abnormalities were diagnosed by ultrasound: Increased nuchal translucency (4.7 mm), increased anteroposterior diameter of the fourth ventricle and increased diameter of the third ventricle of the brain, mesocardia and cardiomegaly. The CVS karyotype revealed 48,XXY,+18 karyotype. In our opinion, the increased anteroposterior diameter of the fourth ventricle of the brain in this fetus was probably an early manifestation of the Dandy-Walker malformation (unproven because of early pregnancy termination), which is typical of Edwards syndrome fetuses. We consider the increased anteroposterior diameter of the fourth ventricle of the brain in the first trimester fetus as an indication for fetal karyotyping and further detailed imaging studies.