Recently, a high incidence of goiter was discovered at Omuro i.n Okitsu Village, a small fishing village facing the Pacific Ocean in Kochi Prefecture in Japan. Since Okitsu Village consists of three separate communities, Omuro, Go and Ura, the incidence of goiter was investigated in each community. In a survey of all 455 children from nursery schools, primary and junior high schools in Okitsu Village, the incidence was 13.4% in Omuro, 3.7% in Go and 1.1% in Ura. The incidence was thus particularly high in Omuro and also the degree of the goiter size in this community was greater than that found in others. In a survey of all 482 inhabitants of the Omuro Community, 39 patients with goiter including 11 cases, which had extremely large goiter, were discovered, the incidence being 8.1%. Cases of goiter were frequently observed in several generations of a single family. The incidence ratio for men to women was 1 to 1.4. Although in this Omuro Community the inhabitants are economically poor and there are frequent cases of consanguineous marriage within the community, there is no noteworthy difference in environmental conditions from those two adjacent communities. Therefore, external factors which are often considered as causes of goiter, such as iodine deficiency in the environment, intake of goitrogen, nutritional deficiency of protein and vitamins, etc. or excess of calcium and fluorine in the soil can hardly be considered as causes of this high incidence. Furthermore, from the fact that the high incidence of goiter runs in families, the cases of goiter reported here may be caused by intrinsic metabolic disorders.