The tailgut is the distalmost portion of the embryonic gut, located caudal to the cloacal membrane. Up to the sixth week of development, it is in close proximity to the distal end of the notochord and the neural tube. It completely regresses by the seventh week, but some caudal duplication-like cysts have been attributed to its remnants. We report a full-term male born with a large heterogeneous sacral mass. Severe bony abnormalities of the coccyx, sacrum and lower lumbar vertebrae were present, but the infant was neurologically intact. At surgery, the upper cystic structures within the mass were found to communicate with the dura, while the solid component, whose surface resembled intestinal mucosal folds, was closely related to the perirectal tissues. The mass was completely resected and the dura oversewn. Since this complex mass contained all three cell lines in an aberrant location, it satisfies the definition of a sacrococcygeal teratoma. However, its unique architecture suggests a malformative, rather than tumoral origin. The macroscopic appearance of this lesion reflects the embryonic relationship between the tailgut, the neural tube and the notochord.