AIMS: To find the optimal cut-off values for cyclin A and Ki67 in early breast cancer tumours and to evaluate their prognostic values. METHODS AND RESULTS: Tissue microarray (TMA) slides were constructed from 570 T1-4 N0-1 M0 breast cancer tumours. The TMA slides were stained for cyclin A and Ki67 using immunohistochemistry with commercial antibodies. To investigate the optimal cut-off values for cyclin A, Ki67 average and maximum values the material was split into two parts at cut-offs defined by dividing it into deciles. For each cut-off value the relative risk (RR) for metastasis-free survival (MFS) and overall survival (OS) was calculated comparing patients with high versus low cyclin A or Ki67 expression. When using a cut-off value around the seventh decile, cyclin A and Ki67 score correlated with the highest RR ratio for MFS in the chemotherapy-naïve subgroup. Among patients having received adjuvant chemotherapy, no statistically significant differences in MFS or OS were found. CONCLUSIONS: The optimal cut-off value for cyclin A average is 8% and for cyclin A maximum value 11%; for Ki67 the corresponding values are 15% and 22%. Additional studies are needed to verify these results.