The overall prevalence of thyroid hormone use in an unselected population of older adults (n = 2575; average age, 68.6 years) was 6.9% (10.0% in women and 2.3% in men). Eighty-one percent of women taking it were doing so for appropriate indications, eg, hypothyroidism, while 12% were not, eg, for obesity or high serum cholesterol; more men (29%) were taking it inappropriately. Inappropriate use was associated with desiccated thyroid more than with thyroxine. After follow-up averaging 6.9 years, 58% of inappropriate users were still taking it. Underuse also occurred. Thirty-seven percent of those definitely hypothyroid had a clearly elevated serum thyrotropin level (greater than 10 mU/L) despite thyroid therapy. Thyroid therapy is common in the elderly; most is appropriate. When inappropriate use occurs, it is more common in men and more often associated with desiccated thyroid, still commonly used in this age group. In chronic users of thyroid hormone, it is important to review currently appropriate indications and to measure serum thyrotropin levels to assess the adequacy of treatment of primary hypothyroidism. [ABSTRACT FROM AUTHOR]