Most papillary carcinomas of the thyroid run a surprisingly indolent clinical course, and even widespread lymph node metastases in the neck are not a bad prognostic omen. A small group behaves in a far more aggressive fashion and kills through local invasion of adjacent structures or blood borne metastases. This paper deals with a papillary carcinoma which does not fit into any of these groups. Following hemithyroidectomy for papillary carcinoma in 1970 the patient, a woman aged 70 years, lived comfortably for nine years until she died of what appeared to be an unrelated cause. During these nine years, papillary carcinoma metastases were removed at irregular intervals from unusual locations such as the thoracic wall, both groins, and the thigh. Gross examination, light and electron microscopy, and freeze-etching, all failed to distinguish this tumor from conventional papillary carcinomas. Morphometry showed that the nuclei were significantly larger than those found in other papillary carcinomas, and conventional and flow cytometric DNA analysis proved that the primary tumor and the metastases contained mainly tetraploid cells. One lymph node metastasis had even larger nuclei than the others and also a different, bizarre DNA distribution pattern. This study also showed that the ground glass appearance of the nuclei of papillary thyroid carcinomas does not depend on hypodiploid DNA values. Of about 70 cases of papillary thyroid carcinomas in the world literature studied by conventional or flow cytometric DNA analysis, this case is the only one with tetraploid DNA values. It is therefore tempting to correlate this tetraploidy to its peculiar biologic behavior.