A survey of endemic goitre in the island of S. Miguel (the Azores) was performed. The prevalence of goitre in school-children varied between 11 and 41%. In the most affected region, 16% of the adult males and 48% of the women had goitre, in some cases grade 3. The median urinary excretion of iodine was very low in school-children, varying between 10 and 49 micrograms I/g creatinine. The reasons for such a low iodine intake in the population of this oceanic island are the scarcity of fish in the diet and, possibly, the leaching of the soil of its iodine content due to high pluviosity.