Purpose: To evaluate the relationship between nuclear DNA contcnts and prognostic factors and survival in breast cancer patients. Materials and Methods: We determined nuclear DNA content from 91 paraffin-embedded malignant breast tumors and evaluated relationship between DNA nuclear content and well-known prognostic indicators of breast cancer and the survival of the patients by statistical analyses. Results: Twenty nine(34.5%) of the 91 tumors examined were diploid, and the remainder(65.5%) contained one or more aneuploid clones. S-phase fraction(SPF) ranged from 1.4 to 68.3%(median 11.2%) and it was higher in aneuploidy tumors than in diploid tumors(p<0.05). Positive axillary lymph nodes were found in 72.7% of the patients who had a tumor with a high SPF (above the median 11.2%) and in 27.3% of those with tumor with low SPF (below median)(p<0.05). The overall survival rate was 96.1% in DNA diploid and 87.6% in DNA aneuploid tumors, showing that DNA ploidy had no prognostic significance in breast cancers. The actuarial survival rates were 96.4% and 86.3% for low and high SPF, respectively(p=0.28). The patients with high SPF showed high disease free survival rate compared to the patients with low SPF but the difference had no statistical significance. Conclusion: Our results indicate DNA aneuploid tumors were more prevalent in breast cancer patients with high SPF or lymph node metastasis and larger patient accumulation with longer follow-up period will be helpful to identifiy the relationship between flow-cytometrical analysis and prognosis.