In patients with subclinical hypothyroidism thyroid hormone therapy should be recommended more often with respect to analysis of effectiveness and risks. There is no cost-difference between treated patients and those who undergo thyroid hormone controls only, but thyroid hormone therapy probably induces improvement of clinical and laboratory parameters and reduction of cardiovascular risk factors. These therapeutic effects have to be elucidated in clinical prospective studies. Thyroid hormone therapy of patients with autoimmune thyroiditis and still euthyroid function obviously inhibits the autoimmune process and development of hypothyroidism. A final recommendation, however, can be given after the data of clinical studies with larger populations are available.