Thyroid disease in the elderly. As people in our society live longer, it is important for clinicians to know more about problems commonly seen in the elderly. Thyroid problems are especially important to understand because they do occur with rather high frequency, and their mode of presentation is frequently different from those seen in younger patients. The thyroid gland does undergo certain age-related changes in anatomy and physiology, but overall the thyroid is able to produce a normal amount of thyroid hormone throughout the years. Hypothyroidism is frequently difficult to diagnose in the elderly, because many of the symptoms of hypothyroidism can easily be confused with symptoms of aging. When hypothyroidism is looked for in large population studies of elderly patients, the incidence varies from 1% to as high as 17%, with women being more commonly affected than men, and subclinical hypothyroidism being more common than overt hypothyroidism. Virtually all cases of hypothyroidism are due to autoimmune thyroid disease, with most patients having measurable titers of thyroid autoantibodies. The therapy of hypothyroidism is done with extreme caution, as older patients are frequently very sensitive to the effects of excess thyroid hormone. In addition, the metabolism of thyroid hormone slows down with age, making the full replacement dose much less in an older patient than in a younger one. Hyperthyroidism is also quite common, occurring in from 0.5% to 3% of all elderly patients. The presentation is frequently atypical, as patients often lack the hyperdynamic symptomatology and instead have a more sedated, apathetic presentation. Weight loss and cardiac symptoms frequently predominate, and the presence of a goiter is frequently absent, making the diagnosis less obvious than in a younger patient. Therapy is usually radioactive iodine, after an adequate course of antithyroid drugs, to render the patient euthyroid. Thyroid nodules do occur with increasing frequency in the elderly, but most of them are not malignant. Fine-needle aspiration for cytology is very helpful in determining which patients should be referred for surgery. Well-differentiated cancers do predominate, but their course is frequently less predictable than in younger patients. Lymphoma of the thyroid and undifferentiated cancers do occur with increasing frequency in the elderly. Multinodular goiter, usually of longstanding, is frequently seen in elderly patients, and thyroid hormone suppressive therapy not only is not indicated but may contribute to exogenous hyperthyroidism. 