We evaluated whether proliferating cell nuclear antigen (PCNA) immunohistochemistry with antigen retrieval could be used as a measure of cell proliferation in archival, formalin-fixed, paraffin-embedded tissues and whether the staining results have long-term prognostic significance in axillary node-negative breast cancer. Primary tumor samples obtained from 109 axillary-node-negative breast cancer cases were used for the study. The best staining results were obtained with the 19A2 antibody after microwave heating in a solution of saturated lead thiocyanate. Using this method, there was a significant correlation (linear regression, r = 0.580, P < 0.001) between the proportion of PCNA19A2-positive carcinoma cells (PCNA19A2 score) and DNA flow cytometric S phase fraction. A high PCNA19A2 score was associated with high mitotic count, DNA aneuploidy, and absence of estrogen receptors. Axillary-node-negative patients with a high PCNA19A2 score (cut-point 8%) had significantly worse prognosis than those with a low PCNA19A2 score (P = 0.008). According to a Cox multivariate analysis, PCNA19A2 score had independent prognostic value but only if S phase fraction was excluded from the analysis. In our study, the PCNAPC10 score correlated weakly only with primary tumor size (analysis of variance) and prognosis (5-year univariate survival analysis), but the significance of these findings needs further evaluation. In conclusion, PCNA immunohistochemistry with the 19A2 antibody after an appropriate antigen retrieval treatment may offer a useful alternative to DNA flow cytometry for the analysis of cell proliferation activity from formalin-fixed, paraffin-embedded breast carcinomas.