OBJECTIVE Evaluation of prognostic significance of nucleolar organizer regions (NORs) in renal cell carcinoma (RCC). METHODS Nuclear organizer regions were quantified in a series of 59 cases of RCC by the silver colloid method, and the NOR index was obtained from the ratio between mean NOR counts in each neoplastic nucleus and in normal nucleus. The patients were staged pathologically and divided into 2 groups by average NOR index of all cases, which was 0.76. Correlations between the NOR index and other parameters were statistically analyzed, and the prognostic value of the NOR index was also examined. RESULTS The NOR indices from each group were correlated with the survival curve. In low stage tumors (pT1 or 2 N0M0), the low NOR index group had a survival rate of almost 100 per cent while in those patients with higher NOR indices, there was a significantly increased mortality (p < 0.01). In patients presenting with high stage tumors (excluding pT1 and 2 N0M0), the survival rate was significantly improved in those patients with a low NOR index (p < 0.01). On the other hand, the patients with a low NOR index have a better prognosis than those with a high NOR index within each tumor grade (p < 0.01). Statistical analysis by the log rank test indicated NORs to be a significant predictor of survival over the whole series within low and high pathological stages and within each tumor grade. Analysis of the data with Cox's proportional hazard model showed that NOR index had a stronger hazard ratio than grade or stage of tumor (p = 0.0005). CONCLUSIONS Our study has demonstrated that NOR index is a new prognostic indicator for patients with RCC (p = 0.0005).