Abstract: Homocysteine (Hcy) is an intermediate product of methionine metabolism and exists in blood in various forms. The pathogenic effect of Hcy in hypertension, immune system, tumor, cardiovascular, and cerebrovascular diseases has been proven since the 1930s. The relationship between Hcy and thyroid diseases has attracted considerable attention from researchers in recent years due to its high correlation with the occurrence and development of various thyroid diseases. The author reviews the research progress of the relationship between Hcy and related thyroid diseases, such as hyperthyroidism, hypothyroidism, chronic lymphocytic thyroiditis, and thyroid cancer.