To the Editor.
—In a review of 453 patients with hyperthyroidism seen in a large thyroid referral clinic between 1970 and 1984 at the Genesee Hospital, Rochester, NY, we found only 11 patients with silent thyroiditis as the causal mechanism, an incidence of 2.4% (Table). This is comparable with that reported by Vitug and Goldman1 in the coastal New York City area and is in contrast to the striking elevations (12% to 23%) reported from authors in Wisconsin2,3 and Ontario.4We are a city located on Lake Ontario and are no longer an endemic goiter locale, since the introduction of iodide in our salt and foodstuffs. It would seem, therefore, that residence by the Great Lakes per se does not necessarily predispose to an increased incidence of thyrotoxic silent thyroiditis. This suggests some other environmental or industrial component may be causally related and, in view of the