Although the predictive value of immature elements in sacrococcygeal teratomas in unclear, there are reports of malignant recurrence after surgical resection of immature sacrococcygeal teratomas. The recurrent tumors are presumed to arise from small residual malignant foci not identified at the time of surgical resection. In this report a premature female infant was delivered at 29 week's gestation with a large sacrococcygeal teratoma. The tumor weighed 1,350 g. It was largely cystic with a focal nodular and variegated appearance. Histologically, the tumor was a grade 1 immature teratoma with a predominance of neuroglial elements. No malignant elements were identified in any of 26 sections examined. The infant died intraoperatively of cardiovascular complications related to the large vascular supply of the tumor but had a grossly complete resection of tumor. At autopsy, a small microscopic focus of yolk sac tumor was identified adjacent to the sacrum anteriorly. Had the infant survived, this focus might well have been a source for malignant recurrence.