Introduction: To treat or not to treat subclinical hypothyroidism is a question, which internationally creates much discussion and writing. Subclinical hypothyroidism is biochemically defined by a serum TSH above the upper reference limit, whereas serum T4 estimates are within the reference range. This pattern of biochemistry indicates a slightly failing thyroid gland. Both subclinical and overt hypothyroidism show large differences in epidemiology between populations, probably caused by a combination of environmental and genetic factors. Whereas there has been consensus on the benefits of thyroid hormone replacement therapy of overt hypothyroidism for more than 100 years, opinions on how to deal with subclinical hypothyroidism are far from unanimous....