Anaplastic thyroid carcinoma is an uncommon carcinoma representing 1 to 4% of all thyroid cancers. The carcinoma is most common in females of the eight decades. It is a locally advanced cancer with frequent infiltration of surrounding organs, blood vessels and skin of neck. Paraneoplastic manifestations could occur. Approximately half of the patients with anaplastic thyroid carcinoma had distant metastasis with lung and brain as the most frequent sites of metastasis. The median survival of patients with anaplastic thyroid carcinoma reported was from 1 to 6 months. The terminology of the cancer in World Health Organization is "anaplastic thyroid carcinoma" rather than "undifferentiated thyroid carcinoma". In the latest American Joint Committee on Cancer (AJCC) TNM staging system for anaplastic thyroid carcinoma, there are updates on T and N categories. To conclude, updated knowledge of clinicopathological features, classification, pathological staging will improve our understanding of the cancer and will help in the management of the patients with this aggressive cancer.