We studied the incidence of thyroid nodules in healthy adults, who had no history of thyroid disease, in Tokushima, Japan, where goiter is not considered endemic. Examination was performed by palpation and using a 10-MHz real-time sonographic scanner. Palpable thyroid nodules were present in two (0.9%) of 227 men and in four (1.8%) of 224 women. On the other hand, nodules were detected by ultrasonography in 42 men (18.5%) and 47 women (21.0%). There was no significant difference in the incidence detected by ultrasonography between men and women in any of the age groups, except in men above 60 years old. It is concluded that thyroid nodules are not an uncommon disorder even in men. Since, clinically, the incidence of nodularity appears to be higher in women than in men, there may be difference between men and women in the development of nodules until they become clinically detectable.