Papillary thyroid cancer (PTC) is a slow-growing tumor with a favorable outcome. Still, some low-risk patients develop local or distant metastases and eventually die from their disease. Many molecular markers are involved in proliferation and apoptosis, including Bcl-2, Ki-67, and p21. Because age over 45 is the most important determinant of a poor survival, we analyzed whether the expression of these tumor proliferation markers differs between young and older PTC patients. Our study comprised 108 PTC patients retrospectively selected by age, i.e. those younger than 35 or older than 55 at diagnosis. Formalin-fixed, paraffin-embedded archival tissue blocks were analyzed for Bcl-2, Ki-67, and p21 protein expression by immunohistochemistry. We showed that expression of Ki-67 increases significantly with age, indicating that tumors in older patients may grow faster. This higher proliferative activity may explain the worse prognosis in these patients. Expression of p21 was higher in large tumors and in tumors extending beyond the thyroid capsule. Expression of Bcl-2 did not correlate with clinical parameters.