Only few studies have evaluated the usefulness of the GLUT1 and p63 status of thyroid carcinomas in revealing tumorigenesis. We studied GLUT1, p53, and p63 immunoexpression in a total of 86 cases of various thyroid carcinoma types to determine the biological significance of GLUT1 and p63 expression in thyroid carcinomas. GLUT1 was detected in six cases of anaplastic carcinoma and in one case of poorly differentiated carcinoma with membranous staining. p63 was detected in five cases of anaplastic carcinoma, in one case of poorly differentiated carcinoma, and in five cases of papillary carcinoma with nuclear positivity. p53 was detected in six cases of anaplastic carcinoma, in one case of poorly differentiated carcinoma, and in one case of follicular carcinoma with nuclear positivity. Five of seven cases of anaplastic carcinoma expressed all three of these markers. The results suggest that GLUT1, p63, and p53 are not expressed in well-differentiated thyroid carcinomas, and that they are usually expressed late in the course of thyroid tumor progression. These data strongly suggest that in anaplastic carcinomas, impairment of p53-mediated repression results in increased GLUT1 and p63 expression, and that this probably reflects the differential regulation of hypoxia-responsive pathways and basal/stem cell regulatory pathways.