Thyroid disorders become more common with advancing age. Clinical features of hypothyroidism overlap with signs and symptoms often present in euthyroid older people and there is high likelihood of misdiagnosis. Conversely, there may be a relative paucity of signs and symptoms in hyperthyroid older people. A large number of patients may have subclinical disease. High suspicion and confirmation by laboratory assay is the key to correct diagnosis, though thyroid function tests should be interpreted with caution during acute illnesses. There is a reduced requirement for levothyroxine replacement in elderly hypothyroid patients and dosage should be titrated up cautiously as it can unmask symptoms of ischaemic heart disease. Drug interactions should be taken into account because a number of drugs interfere with levothyroxine absorption and metabolism. Radioactive iodine ablation of overactive thyroid tissue is the preferred treatment of hyperthyroidism in older people.