We have reviewed the available literature on thyroid diseases and coronavirus disease 2019 (COVID-19), and data from the previous coronavirus pandemic, the severe acute respiratory syndrome (SARS) epidemic. We learned that both SARS and COVID-19 patients had thyroid abnormalities. In the limited number of SARS cases, where it was examined, decreased serum T3, T4 and TSH levels were detected. In a study of survivors of SARS approximately 7% of the patients had hypothyroidism. In the previous evaluation evidence was found that pituitary function was also affected in SARS. Others suggested a hypothalamic-pituitary-adrenal axis dysfunction. One result published recently indicates that a primary injury to the thyroid gland itself may play a key role in the pathogenesis of thyroid disorders in COVID-19 patients, too. Subacute thyroiditis, autoimmune thyroiditis and an atypical form of thyroiditis are complications of COVID-19. Thyroid hormone dysfunction affects the outcome by increasing mortality in critical illnesses like acute respiratory distress syndrome, which is a leading complication in COVID-19. Angiotensin-converting enzyme 2 is a membrane-bound enzyme, which is also expressed in the thyroid gland and the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) uses it for docking, entering as well as replication. Based on the available results obtained in the SARS-CoV-2 pandemic, beside others, we suggest that it is necessary to monitor thyroid hormones in COVID-19.