Aberrations in the G1-S transition have been observed in several malignancies, suggesting that cell cycle defects are linked to the activation of oncogenes and inactivation of suppressor genes involved in the transformation process. The frequency of G1/S aberrations in human renal cell carcinoma (RCC) has not been fully clarified. We have therefore analyzed the cyclin E content, using Western blotting, in 79 RCC and 12 corresponding kidney cortex tissues as well as the fraction of p27-positive cells in 73 RCCs, using immunohistochemistry. Most of the tumors (65%) exhibited higher cyclin E levels than corresponding normal kidney cortex tissues. However, only a small fraction of the tumors (3 of 80) had excessive levels of cyclin E when cyclin E levels were compared with proliferation. Cyclin E levels higher than the median value were associated with aneuploidy (p = 0.025), high stage (p = 0.027), high grade (p = 0.013) and high erythrocyte sedimentation rate (ESR; p = 0.005). Cyclin E was further inversely correlated with cyclin D1 (p = 0.023) and positively correlated with cyclin D3 (p = 0.003). Most tumors (76%) demonstrated a normal fraction of p27-positive cells. There was an inverse correlation between p27 positivity and tumor size (p = 0.007), despite a lack of correlation between p27 and proliferation. Patients with p27 low tumors had a poor survival (p = 0.002). There was no correlation between p27 and cyclin E levels. In summary, the results suggest that protein expression of cyclin E and/or p27 is linked to tumor behavior. Copyright 2002 Wiley-Liss, Inc.