BACKGROUND. The prognostic value of Fuhrman nuclear grade for patients with renal cell carcinoma has been well-characterized. However, to the authors' knowledge, the prognostic significance of the amount of high-grade renal cell carcinoma has not been previously analyzed. METHODS. The authors identified 898 consecutive renal cell carcinoma cases treated with nephrectomy between 1989 and 2003. Histopathologic features that were captured based on re-review of all slides included histologic type, pathologic stage, conventional Fuhrman grade, and percentage of Fuhrman grade 3 and 4 carcinoma, as ascertained by visual inspection of histologic slides. The clinical endpoints were metastasis-free survival, cancer-specific survival, and overall survival. RESULTS. Kaplan-Meier analysis demonstrated that both conventional Fuhrman grading and the percentage of Fuhrman grade 3 and 4 carcinoma were highly correlated with all 3 measures of patient survival (P < .0001). The creation of 3 categories of the percentage of Fuhrman grade 3 and 4 carcinoma (0%, 1-50%, and 51-100%) generated distinctly separate survival curves. On Cox proportional hazards multivariate analysis, TNM stage, tumor size, and the percentage of Fuhrman grade 3 and 4 carcinoma were all found to be significantly associated with all 3 types of patient survival (all P values <.05). CONCLUSIONS. The determination of the percentage of renal cell carcinoma that is 0%, 1% to 50%, or 51% to 100% high Fuhrman grade 3 and 4 is a simple and powerful measurement of patient outcome after surgery that provides additional prognostic information beyond stage, tumor size, and conventional Fuhrman grade. This prognostic information could be useful in the stratification of patients into prognostic groups for the development of more individualized follow-up schedules and for enrollment into clinical trials.