We examined HLA association with differentiated thyroid carcinoma in 45 patients from Newfoundland. No association was found. This finding contrasts with the description of an association of thyroid cancer with HLA-DR1 in Italy and Hungary (iodide deficient areas) and with DR7 in the American mid-west. We suggest that iodide deficiency predisposes DR1 + individuals to thyroid cancer and that this risk is negated by iodide sufficiency unless some other risk factor supervenes.