['Although papillary thyroid carcinoma (PTC) generally has an indolent nature, massive extrathyroid extension (Ex) and clinical lateral node metastasis (N1b) are prominent predictors of a dire prognosis. However, it remains unknown whether these factors affect patient prognosis with uniformity. In this study, we investigated the relationships between the prognostic impact of these factors and carcinoma size.', 'A total of 5,917 patients who underwent initial and curative surgery for PTC between 1987 and 1995 were enrolled in this study. After dividing these patients into four subsets based on tumor size--≦1.0 cm, 1.1-2.0 cm, 2.1-3.0 cm, and >3.0 cm--we investigated the prognostic impacts of Ex and N1b in each subset.', 'Relative risk (RR) of disease-free survival (DFS) of N1b was the highest in the subset ≦1.0 cm and decreased with tumor size. RR of Ex was smaller in carcinoma ≦3.0 cm but larger in carcinoma >3.0 cm compared with that of N1b in the respective subsets. On multivariate analysis, N1b was a more important prognostic factor than Ex in carcinoma ≦3.0 cm, but the prognostic impacts of these two factors were reversed in carcinoma >3.0 cm. Similar findings were obtained in analyses for cause-specific survival (CSS) and prognostic value of N1b was more significant in carcinoma ≦3.0 cm but less significant in carcinoma >3.0 cm than that of Ex.'] Do prognostic impact of extrathyroid extension and clinical lymph node metastasis in papillary thyroid carcinoma depend on carcinoma size?