The analysis of ploidy provides valuable information allowing a more precise diagnosis, a more dependable prognostic and the choice of appropriate therapy. With ploidy analysis one can assess the aggressiveness of a given tumor. Aneuploidy of tumors clearly indicates a significantly lower patient survival index. Ploidy analysis of tissue sections yields a clear overall indication of the proportion of cells exhibiting hyperploidy within the tumor mass. The application of this approach is amenable to diverse types of tumors including colo-rectal neoplasias. Additionally, it provides a correlation with the histological presentation of each tumor. The study includes DNA ploidy analysis of 212 patients with primary adenocarcinoma. Sixty-four of the cases examined had follow-ups of a least 2 years. Eighteen of this group had diploid non-proliferating tumors, of which 2 (11%) subsequently died. Nineteen of the 64 had proliferating diploid tumors, 11 (58%) of whom died within the follow-up periods. Twenty-seven patients had tumors which were clearly aneuploid, 12 (45%) of whom later died. Our study demonstrates the prognostic value of ploidy analysis. The preliminary results indicate that mortality of patients with proliferating tumors is approximately 50% after 2 years. This prognostic is independent of other more classical criteria of tumor staging, namely Dukes' classification, histological differentiation and size of tumor. In the near future, ploidy analysis should be introduced as a standard part of tumor assessment. It clearly provides a valuable prognostic allowing the selection of patients requiring a careful follow-up.