• The difficulties of making a diagnosis of chordoma are illustrated by the roentgenographic findings in 20 cases. In 10 cases the lesions arose from the base of the skull, 6 lesions were vertebral and 4 sacrococcygeal. The clinical findings and differential diagnosis will vary with the level of the lesion. Chordomas are slow-growing and destructive. A striking extraosseous component often is present, and this softtissue mass may predominate over the bony changes as demonstrated in roentgenograms. Because chordomas are usually lacking in distinctive features, preoperative diagnosis is uncommon.