Background: Confusing data have been presented for the breast cancer cancer patients on correlations between DNA ploidy and the percentage of S-phase cells and other prognostic factors. The aim of this study was to compare DNA ploidy and the S-phase fraction with traditional prognostic factor to evaluate the prognostic significance of DNA ploidy and SPF. Methods: We performed flow cytometry on archival paraffin blocks of primary breast cancers from 449 patients. The DNA ploidy and the SPF were examined along with tumor size, the status of lymph node metastasis, age, status of hormonal receptor, histologic grade, tumor type to evaluate clinical utility of DNA ploidy and SPF. Results: The results of the DNA ploidy and SPF revealed 166 diploidy (37%), 283 (63%) aneuploidy tumors. The DNA ploidy status correlated significantly with the status of lymph node metastasis and tumor size. No significant correlations were found with age, histologic grade, or ER receptor status. The S-phase fraction correlated significantly with the ER receptot status. No significant correlations were found with age, tumor size, status of lymph node metastasis, histologic grade, tumor type. Conclusions: An increased incidence of aneuploidy was found in tumors from patients with positive axillary lymph nodes, larger tumor size and increased incidence of higher S-phase fraction was found in tumors from patients with negative ER receptor. To evaluate the clinical utility of these factors, it will be necessory to measure them on a larger number of patients, so that multivariate survival analyses can be performed.