The occurrence of a fetal tumor is rare, 50% of all fetal tumors being sacrococcygeal teratomas. Prenatal diagnosis of this condition is important for the monitoring of the affected fetuses and for establishing the mode and time of delivery. We describe two cases of fetal sacrococcygeal teratoma diagnosed by 2D- and 3D-ultrasound. Three-dimensional ultrasound proved to be useful both in the diagnosis and patient counseling. The combination of 2D- and 3D-ultrasound enables the diagnosis to be made during the first trimester of pregnancy.