Papillary thyroid carcinoma is a frequent thyroid cancer. Many factors have been reported to be of prognostic importance, but the significance of biologic factors suggesting aggressiveness and proliferating activity has not been sufficiently documented. Conventional prognostic factors such as age, extrathyroidal invasion, lymph node and distant metastasis, and biologic factors including histologic differentiation, DNA ploidy, S-phase and G2M-phase fractions, and expression of CD44 variant 6 (CD44-v6) obtained from 131 patients who underwent surgery for papillary thyroid carcinoma at Osaka Police Hospital were analyzed retrospectively. Age was closely related to extrathyroidal invasion, G2M-phase fraction, and CD44-v6 expression. Extrathyroidal invasion was independently related to age, gender, and lymph node metastasis. The grade of lymph node metastasis was related to extrathyroidal invasion, gender, distant metastasis, and CD44-v6 expression. Distant metastasis was associated with aneuploid tumors. Cause-specific survival was independently related to biologic factors including extrathyroidal invasion, distant metastasis, DNA ploidy and S-phase fraction. These results suggest that biologic factors indicating aggressiveness and proliferating activity are important for papillary thyroid carcinoma.