A review was undertaken of the clinical, gross, and microscopic features of thyroid carcinoma in all patients younger than 21 years of age seen at North Carolina Memorial Hospital from 1952 to 1987 (N = 32). These patients had papillary carcinoma, well-differentiated follicular carcinoma with Hürthle cell change, medullary carcinoma, and an unclassifiable aggressive malignancy. In spite of the presence of lymph node metastases at diagnosis in more half the patients with papillary carcinoma, the prognosis of pediatric papillary thyroid carcinoma appears to be excellent with treatment by surgical debulking and hormonal thyroid suppression. Flow cytometric study of 26 cases showed tumor aneuploidy in 8 of 21 papillary carcinomas and 2 of 3 follicular carcinomas. Aneuploidy did not, however, correlate with clinical outcome in this group of pediatric patients, who were followed for 1 to 29 years. Analysis of multiple tissue blocks of tumor does appear to increase the probability of identifying aneuploid populations.