The prevalence of thyroid dysfunction in the elderly is reported to be markedly high, at least in some Western countries in which iodine intake is sufficient or increased because of recent supplementation of iodine for public health. We therefore wished to investigate the prevalence of thyroid dysfunction among elderly people in an endemic goiter area. The study included 198 subjects over the age of 55 years. It was carried out in two towns 20-30 km, south of Kayseri, Central Anatolia. Questioning on medical history, physical examination and grading of thyroid gland size were performed. Serum TSH was measured by a sensitive immunoradiometric assay. Serum free thyroid hormones and thyroid autoantibodies were measured in the subjects with TSH concentrations below 0.4 mu IU/ml or above 4.5 mu IU/ml on the initial screen. Drinking water was also analysed for iodine content. Twenty-five (12.6%) subjects had either elevated (6.5%) or suppressed (6.1%) serum TSH levels. No patient had clinical hypothyroidism (high TSH and low free thyroxine and free triiodothyronine). Three (1.5%) subjects had clinical hyperthyroidism (low TSH and high free thyroxine and free triiodothyronine). Only one subject was positive for antimicrosomal and antithyroglobulin antibodies. The prevalence of goiter was 25.8%. The iodine level in drinking water was found to be 3 micrograms/L. In conclusion, we believe that the prevalence of thyroid dysfunction in the elderly may depend on the iodine status in the environment. We think that hyperthyroidism due to multinodular goiter is more important than hypothyroidism for elderly people living in an endemic goiter area, probably due to the low frequency of autoimmune thyroid disorders.