The aim of this work was to study the prevalence of thyroid disease in pregnant and puerperal women and newborns in Pirque (Chile) and its possible relation to iodine intake or autoimmune disease. Two hundred twenty eight women with 13.4 +/- 3.4 weeks of pregnancy were examined initially and in 223, laboratory tests were performed. Goiter was found in 107 women. Although all women were euthyroid, those with goiter had higher serum levels of T3 and T4. Nineteen women had positive anti-thyroid antibodies and urinary iodine excretion was > 100 micrograms/g creatinine in 87.2%. Within 2 and 57 weeks after delivery (mean 13.5 weeks), 183 women were reexamined and in 175 laboratory tests were performed. Serum T3 continued to be higher in those with goiter. Fifteen women with positive anti-thyroid antibodies during pregnancy continued to have positive titres; of these, two had a post partum thyroiditis and one a graves disease. Two hundred three newborns were examined and no one had goiter or elevated TSH. It is concluded that there is a high frequency of goiter among pregnant and puerperal women from Pirque, that iodine intake is normal and that there is a low frequency of post partum thyroiditis.