Our results suggest a link between increased iodine intake and hypothyroidism. Similar resultswere reported in small-scale comparative epidemiologic studies by Laurberg et al.15 and Szabolcset al.16 No significant difference in the cumulative incidence of overt hypothyroidism was observed among the three cohorts. This finding mayrelate to the short interval between the baselineand follow-up studies and the long latency periodfor hypothyroidism. As compared with regionssuch as Panshan, in which inhabitants have amildly deficient long-term intake of iodine, thereappears to be a higher incidence of both overt andsubclinical hypothyroidism in regions such asZhangwu, where iodine intake increased from being mildly deficient before salt iodization to morethan adequate afterward. Moreover, the highest