It has been known for over 50 years that the amount of nuclear chromatin (DNA) in malignant neoplasms differs from that of homologous normal cells (1 ). More recently, it has been shown that nuclear DNA content correlates with the clinical outcome of various human neoplasms including urologic malignancies (2 –10 ). An important problem in the care of patients with renal cell carcinoma (RCC) is the prediction of the neoplasms malignant potential, and in turn the patient’s prognosis. Various parameters have been used to assess the malignant potential of renal cell carcinoma, including clinical and pathologic stage, histologic grade, tumor size, nuclear morphology, immunohistochemistry, age, elevated erythrocyte sedimentation rate, and hypercalcemia. To date, the most important predictors of prognosis in patients with RCC have been tumor pathologic stage, histologic grade and type (11 ,12 ). However, it has been shown that patients within a specified stage and grade may differ in their disease progression and survival (13 ,14 ). Furthermore, none of these variables alone or in combination has shown to provide total reliable prognostic information for the individual patient. These reasons led several groups to evaluate the prognostic value of nuclear DNA content in patients with renal cell carcinoma.