Résumé : OBJECTIVE: To investigate the prognostic value of nuclear DNA content (DNA ploidy level) in a series of 95 renal cell carcinomas (RCCs). STUDY DESIGN: Eight variables were used to characterize DNA ploidy levels. They included DNA index and seven others characterizing the presence of specific stem cell lines in each of the 95 RCCs under study. All these variables were determined by means of computer-assisted microscopy applied to Feulgen-stained nuclei. The actual information contributed by each of the eight variables was determined by means of univariate statistical analyses. RESULTS: The results showed that in the DNA ploidy-related eight variables, the presence of at least 4% aneuploid nuclei with > 5C DNA content was associated with the most significant prognostic value in RCCs with intermediate (T2, T3) invasion levels. CONCLUSION: The present study clearly showed that stem cell line characterization, and particularly the presence of highly aneuploid cells (with > 5C DNA content), is associated in RCCs with significant prognostic value. This kind of marker may help the identification of patients who will develop metastases after surgery and for whom adjuvant therapy might thus be indicated.