Ninety-seven newborn infants, who were referred because of positive TSH results at screening for congenital hypothyroidism (CH), underwent ultrasonography (US) of the thyroid. US findings were classified into four groups: A) undetectable thyroid (n=7, 7.2%), B) significantly enlarged thyroid (n=5, 5.2%), C) unilaterally small thyroid (n=2, 2.1%), and D) normal thyroid (n=83, 85.5%). All 12 cases in groups A and B had TSH levels higher than 30 μU/ml at the screening, and 11 of them had elevated confirmatory TSH levels exceeding 50 μU/ml. In one patient in group A and both patients in group C, the serum TSH levels remained mildly elevated. Thus, all infants with abnormal US findings showed persisting abnormal TSH levels, although some showed only mild elevation. By contrast, among the 7 infants in group D with high TSH levels (>30 μU/ml) at the screening, 4 of them subsequently showed transient elevation of serum TSH levels. In conclusion, abnormal US findings of the thyroid were associated with abnormal thyroid function and a subsequent requirement of therapy. Thyroid US provides useful information for the management of infants screened for CH.