Since morphological features of renal cell carcinomas may not always predict their clinical behaviour, other biological parameters are more and more searched for, as prognostic indicators. Among those, the Authors evaluate the cytokeratin-vimentin intermediate-sized filaments co-expression in a series of 32 renal carcinomas and analyze this feature in correlation with both traditional criteria and proliferative activity of tumor cells, studied by means of the proliferation cellular nuclear antigen (PCNA) expression as well as of the nucleolar organizer regions (NORs) count, within tumor cells. From this study, nuclear grade stands out as the best parameter which, furthermore, shows a significant relationship with the cytokeratin-vimentin co-expression and the mean NORs count in tumor cell populations. Further investigations about relationships between these parameters and survival of the patients, who, at present, are almost all alive, will be performed afterwards.