Background. Owing to their rarity, the Prognostic ramifications of thyroid metastases from renal cell cancer are unclear. Methods. This retrospective analysis comprised 17 patients who underwent thyroid surgery (15 total thyroidectomies, 2 lobectomies) for renal cell cancer metastases. Results. The mean follow-up after thyroid surgery was 65 months. Seven of the 9 deaths involved patients with extrathyroidal metastatic growth despite previous locally curative resection in all but I patient. There was a strong relationship between extrathyroidal growth and recurrent laryngeal nerve invasion (57 vs 0%; P = .015), cervical lymph node metastasis (71 vs 0%; P = .003), the number of positive neck nodes (means of 1 vs 0 nodes; P = .0.14), laryngeal, tracheal or esophageal invasion (43 vs 0%; P = .05), and internal jugular vein invasion (43 vs 0%; P = .05). Powerful effects on cause-specific mortality after thyroid operation for renal cell cancer metastases were seen fir extrathyroidal growth (means of 15 vs 69 months; P = .004) and recurrent laryngeal nerve invasion (means of 10 vs 56 months; P = .002). Conclusion. Extrathyroidal metastatic growth reflects an aggressive tumor biology, which may extend to other-renal cell cancer metastases outside the neck. In. this setting, extensive surgery aimed at preventing local complications should be embedded in a systemic treatment concept. (Surgery 2010;147:65-71.)