Numerous pathohistologic criteria, difficulties and pitfalls in the process of diagnosing of thyroid carcinoma are discussed. Benign hyperplastic papillae may be present in colloidal cystic goiter and hyperplastic goiter. These structures are lined by cells with normochromatic nuclei and do not disturb the thyroid tissue architecture. Papillae in papillary thyroid carcinoma have cells with ground-glass, hypochromatic nuclei. Follicles inspissated in capsula of follicular or even colloidal adenoma may be evaluated as capsular invasion--diagnostic feature of follicular carcinoma. Undifferentiated thyroid carcinoma is sometimes similar to fibrosarcoma and reveal cellular pleomorphism, anaplasia and numerous foci of necrosis. Medullary thyroid carcinoma with scanty stromal amyloid, its papillary variant and carcinoid-like histologic type consist of oval cells with eosinophilic cytoplasm and dark nuclei.