​Background: Inadequate intake of iodine leads to insufficient production of thyroid hormones, which adversely affects the developing brain resulting in the disease states collectively known as Iodine Deficiency Disorders. Although the association between ocean proximity and iodine environmental availability is well recognized, recent studies have revealed an inadequate iodine intake in the Azorean islands. Objectives: We investigated the possible underlying causes of iodine environmental availability in these oceanic islands and its association with iodine intake in schoolchildren. Methods: Iodine concentration in soil and grass pasture was measured by INAA and in drinking water by spectrophotometry. Urinary iodine concentration (UIC) in schoolchildren was assessed by ICP-MS in a randomized crosssectional survey with 315 participants from S. Miguel (study group) and Sta. Maria islands (reference group). A validated diet questionnaire assessing sources of iodine was recorded. Data were analyzed with logistic regression models, adjusting for confounding factors (age, residence time, dairy products and meat consumption). Results: The iodine concentration in reference soils was significantly higher than in the study group (58.1 ppm vs. 14.5 ppm, respectively; p=0.001). Similarly, the schoolchildren with inadequate UIC was significantly higher in the study group than in the reference one (63.0% vs. 37.8%, respectively; p<0.001). Chronic exposure to low iodine bioavailability was significantly associated to the exacerbation in iodine deficiency severity, with a 4.9-fold increased risk in the study group. Conclusions: The differences observed in the studied islands are related with each island geomorphology (soil properties and orography) and climate, which can promote or inhibit iodine environmental availability, contributing distinctively to iodine bioavailability and human intake.