Histological grading of teratomas is a useful method for evaluating patient prognosis. Although this has been repeatedly shown with ovarian teratomas, those of the sacrococcygeal area have not been scrutinized to a comparable extent. We believe that histologic grade and clinical behavior correlate closely in congenital sacrococcygeal teratomas. Correlation with clinical staging is less clear. There are some taxonomical and conceptual problems posed by the congenital nature of these tumors. The worst prognosis is dictated by the presence of yolk sac tumor areas, which was seen in seven of 40 teratomas examined. Although a neuroectodermal component is common, and was here proved to have metastasizing capacity, its inherent tendency may be toward spontaneous self-limiting differentiation. Vitelline differentiation, however, seems to imply irreversible progression and a uniformly bad prognosis.