With the wide application of thyroid function tests performed in current clinical medicine, including field of preventive medicine, subclinical hypothyroidism has become an increasingly recognized clinical entity in daily practices encountered by physicians in general practice and subspecialties, including endocrinologists and geriatricians. The diagnosis may not be difficult since measured levels of thyroid-stimulating hormone (TSH), by definition higher than the upper normal limit of the laboratory references, and free thyroxine (fT4) within the normal reference range can provide enough biochemical evidence for a tentative diagnosis, although repeated tests are often required for confirmative purpose due to the largely unpredictable natural course of this endocrine disease. The presence of autoimmune antibodies (especially thyroid-peroxidase antibodies) significantly increases the risk of future development into overt hypothyroidism. Beyond that, challenges in clinical scenario, especially in the elderly population, may lie in the decision of providing optimal management by administration or not of levothyroxine supplement therapy, even when a diagnosis has been given. Indications for treating subclinical hypothyroidism include a desired improvement in symptoms, prevention of adverse events associated (especially the cardiovascular disorders), as well as prevention of overt hypothyroidism. Current guidelines from academic societies recommend that, in those with TSH levels ≥ 10 uIU/mL, small doses (eg, 25-75 μg per day) of levothyroxine usually suffice to restore normal serum thyrotropin levels in the majority of non-pregnant patients. The targets of TSH levels are recommended to set by age groups: for younger patient (< 60 years): 1-2.5 uIU/mL, whereas enlarged to 3-4 uIU/mL in patients between 60-70 years and 4-6 uIU/mL when older than 70 years. However, these potential benefits of levothyroxine supplementation should be weighed against the risks of reducing thyrotropin values below the reference range and potentially causing iatrogenic subclinical or overt hyperthyroidism.  (J Intern Med Taiwan 2022; 33: 203-217)