Glucose transporter-1 (GLUT-1) expression was immunohistochemically analysed in a total of 268 cases of thyroid gland disease, including 129 cases of papillary carcinoma (PC), 60 cases of follicular carcinoma (FC), 57 cases of follicular adenoma, and 22 cases of adenomatous goitre. Seventy-one percent (91/129) of PC cases showed GLUT-1 expression, semi-quantitatively evaluated as: +, 21 cases (16%); 2+, 37 cases (29%); 3+, 33 cases (26%); and negative, 38 cases (29%). These positive cases were divided into two groups: 'membrane-like' pattern in 24 cases (19%), and 'cytoplasm-predominance' pattern in 67 cases (52%). GLUT-1 expression was observed in 5% (3/60) of FC cases, but all follicular adenomas and adenomatous goitres were negative for GLUT-1 (PC vs. FC, p<0.0001). Membrane-like expression was observed more frequently in non-organ-confined PCs (pT4) than in organ-confined PCs (pT1, 2, and 3) (p=0.0056). Seventy-five percent (18/24) of PC cases showing membrane-like expression were non-organ-confined. The membrane-like pattern was observed more frequently in PCs with lymph node (LN) metastasis compared to those without (p=0.0036). Ninety-two percent (22/24) of PC cases showing the membrane-like pattern were not organ-confined. Semi-quantitative analysis of glut-1 mRNA by RT-PCR showed a tendency toward higher expression in PCs compared to FCs, follicular adenomas and adenomatous goitres, and the mRNA expression in PCs with a membrane-like pattern was higher than those showing cytoplasm-predominance. We concluded that: 1) GLUT-1 is immunohistochemically useful in distinguishing PC from FC and benign diseases; 2) GLUT-1 may play an important role in the advancement of PC and LN metastasis, and its membrane-like expression is of more clinical significance than the cytoplasm-predominance pattern; and 3) glut-1 mRNA expression corresponds with the immunohistochemical expression profile.