RAS mutations (HRAS, NRAS and KRAS) are found in all epithelial thyroid malignancies. The frequency of KRAS mutations in thyroid carcinomas is 2-3%. Overall, RAS mutations are identified in 10--20% of papillary carcinomas (follicular variant), 40--50% of follicular carcinomas and 20--40% of poorly differentiated and anaplastic carcinomas. Of note, RAS point mutations are mutually exclusive with other thyroid mutations such as BRAF, RET/PTC, or TRK rearrangements in papillary thyroid cancers. In follicular carcinomas, RAS mutations are mutually exclusive with PAX8-PPARG rearrangements. RAS mutations have also been associated with more aggressive disease and distant metastasis. The therapeutic implications of RAS mutations in thyroid cancer are unknown at this time.