To determine the influence of age on the signs and symptoms of hyperthyroidism we prospectively examined 880 patients and matched them by age, sex, race, and visit date with similarly examined euthyroid control subjects. Many signs and symptoms showed little change with age until after the fifth decade of life when they began to decrease gradually. Findings that increased with age were weight loss and atrial fibrillation, while those that decreased most markedly with age were increased appetite and weight gain. The diagnosis is more difficult as age progresses because there are fewer findings and because the significance of those present may not be appreciated. Identification of the most sensitive and specific signs and symptoms in each age decade should improve the early detection of hyperthyroidism.