Renal cell carcinoma (RCC) is known to display a wide variation in biological behavior and clinical outcome. Although usual bioclinical prognostic parameters (eg, nuclear grade, tumor stage) are to a certain extent useful in predicting the outcome of RCC after radical nephrectomy, they now appear to be insufficient. The polyamines (spermidine, spermine, and putrescine) are ubiquitous polycations that are essential for cell proliferation. To support their excessive proliferation, cancer cells have high rates of polyamine metabolism. Indeed, malignant cells typically have higher polyamine levels than their normal counterparts. Before this report, antipolyamine antibodies that are potentially valuable tools for the in situ observation of polyamines had not been exploited in clinical conditions. In the present study, tumor tissues obtained from radical nephrectomy performed for RCC (n = 73) were immunostained with the anti-spermine monoclonal antibody Spm8-2, and the immunoreactivity was evaluated as a prognostic tool. RCC cells displayed various reactivity to the antibody Spm8-2 that translated into a heterogeneous cytoplasmic staining. The prognostic value of the labeling index (LI) on clinical outcome was correlated with the usual clinicopathologic parameters, and the cell proliferation rate was evaluated using Ki-67 labeling. Multiple correspondence analysis and ascending hierarchical classification were performed to determine significant prognostic factors. Univariate statistical survival analysis demonstrated that tumor size (P < .001), nuclear grade (P < .01), necrosis (P < .007), tumor stage (P < .004), metastasis (P < .001), Ki-67 LI (P < .0003), and Spm8-2 immunoreactivity (P < .0001) were predictors of tumor-related death. A positive correlation was found between Ki-67 LI and Spm8-2 immunoreactivity (r' = .53). Multivariate analysis revealed that only Ki-67 LI and Spm8-2 immunoreactivity were significant independent factors in patients with metastases (P < .04 and <.001, respectively) and in patients without metastases (P < .006 and <.001, respectively). Moreover, 100% of the patients with Spm8-2 immunoreactivity <10% were alive at the end of the follow-up. In terms of predictive values, Spm8-2 immunoreactivity had the highest predictive values (sensitivity, 89; specificity, 75; risk ratio, 11) of all clinicopathologic parameters. This study demonstrates that the anti-spermine monoclonal antibody Spm8-2 may be used at the time of radical nephrectomy as a reliable prognostic marker for defining RCC patients at high risk for progression.