The prevalence of diabetes has nearly doubled since 1980, mounting from 4.7% to 8.5% in overall adult population. Thyroid disorder is another common endocrine disorder with prevalence of hypothyroidism as much as 4.6% and hyperthyroidism as much as 1.3% in population according to the National Health and Nutrition Examination Survey. These two most common endocrinopathies often co-exist and mutually influence each other. They have complex links of abnormal biochemical pathways, unregulated genetic expression of many genes and hormonal malfunctions. Thyroid hormones affects the regulation of carbohydrate metabolism, lipid metabolism and pancreatic function, and on the other hand, diabetes affects thyroid function tests to variable extents. In this review article we emphasized the epidemiology of diabetes and thyroid disorders, classification of thyroidism, and finally the impact of thyroidism to the various aspects of glucose and lipid metabolism in diabetics.