We suspected two fetuses of having sacrococcygeal teratomas following initial two-dimensional ultrasound scanning at 18 and 22 weeks' gestation. The fetuses were then scanned with three-dimensional multiplanar surface and three-dimensional orthogonal planar ultrasound to establish a definitive diagnosis. Although we made a presumptive diagnosis in both cases after initial two-dimensional scanning, with three-dimensional ultrasound we were better able to define the degree of involvement of the sacrum and other pelvic structures of prognostic importance.