Subclinical hypothyroidism (SCH) is a relatively common endocrine condition characterised by raised serum thyrotropin (TSH) levels in the presence of normal circulating thyroid hormones. It is generally recognised that SCH especially if it is sustained - is a mild form of hypothyroidism but whether it should be treated or not is a matter of a long-standing debate amongst both paediatric as well as adult endocrinologists. In adults, there are conflicting data on the long-term outcomes of SCH with some studies suggesting adverse metabolic, cardiovascular, pregnancy-related and quality of life outcomes. On the other hand, there is emerging evidence to suggest that SCH may not be detrimental to health (or may even be beneficial) in the very elderly. Clinical trials of treatment of SCH have mostly shown modest benefit in reduction of cardiovascular risk factors: mainly dyslipidaemia, but little or no improvement in other areas. Therefore, current evidence does not support the view that all patients with SCH should be treated. However, there may be certain groups of individuals that may gain from treatment in adult populations. This overview will identify such groups that may be at risk of the adverse effects of SCH and could potentially benefit from treatment. Furthermore, how the lessons learnt from adult SCH populations could be applied to younger groups will be discussed.