The objective of this study is to access the prevalence of diffuse thyroid disorders by using ultrasonography in healthy adults. Among 1535 adults who underwent thyroid ultrasonography, thyroid disorders were detected in 191 subjects (12.4%). There was a rapid increase of thyroid functional abnormalities in addition to subclinical thyroid disease with more than 3 features of diffuse thyroid disorder. Therefore we suggest that the thyroid function test and thyroid auto-antibodies should be checked when there are more than 3 features of the diffuse thyroid disorder in ultrasonographic examination, even if the patient does not have any symptoms.