The AJCC Cancer Staging Manual, Eighth Edition (AJCC 8th edition) contains a number of significant changes, many of which affect the reporting of clinicopathologic parameters in thyroid cancers. The first key change is the separation of medullary thyroid carcinoma into its own chapter. Within differentiated and anaplastic thyroid carcinomas, anaplastic carcinomas are now assigned a T stage similar to differentiated thyroid carcinomas. However, this is largely cosmetic because these are still assigned stage group IV. Perhaps the most significant alteration from a reporting standpoint is revision of extrathyroidal extension (ETE) in terms of T staging. Pathologic stage pT3 is now subdivided into pT3a (by size) and pT3b (by ETE). Under AJCC 8th edition, pT3b is now defined by gross (clinical, radiologic, and/or macroscopic) ETE. Other key changes are the inclusion of level VII (anterior mediastinal) lymph nodes as N1a and changes in stage groupings, particularly with a new age cutoff of 55 years, and a downshift in several stage groups. In medullary thyroid carcinoma, the potential prognostic value of nonanatomic factors (ie, serum calcitonin, carcinoembryonic antigen, RET mutation status) is officially recognized, although not yet part of staging. The advent of the new terminology noninvasive follicular thyroid neoplasm with papillary-like nuclear features will remove a subset of tumors that qualify for this new designation from formal AJCC staging altogether.