Background: The eighth edition of the American Joint Committee on Cancer tumour, node, and metastasis staging system did not take T stage into consideration when evaluating Stage IV C medullary thyroid carcinoma (MTC) patients. The aim of this study is to investigate the clinical outcomes and implications of T stage in this population. Methods: Eligible patients from the Surveillance, Epidemiology, and End Results database and the Department of Thyroid Surgery in West China Hospital of Sichuan University and who were diagnosed with Stage IV C MTC were included in this study. The overall survival (OS), the cancer-specific survival (CSS), and the precise cause of MTC-induced death were analysed. The potential risk factors, including the T stage, in the OS and CSS were evaluated by univariate and multivariate Cox regression models.Results: This retrospective study enroled 204 Stage IV C MTC patients. The 5-and 10-year OS rates were 31.8% and 17.1%, respectively, and the 5-and 10-year CSS rates were 40.4% and 22.5%, respectively. More importantly, the rates of MTCinduced death between primary or distant metastatic lesions in Stage IV C MTC patients were comparable in our institution. Additionally, the univariate and multivariate analyses demonstrated that the presence of an advanced T stage was an independent prognostic factor for both the OS (T4 vs. T1-T3, hazard ratio [HR]: