The aim of this study was to look for correlations between nuclear DNA content of colo-rectal tumors, and such clinical parameters as age, sex, location, CEA, histological grade and Duke's stages. A prospective study is carried out on surgical patients, subjected to standard criteria of radicality. Nuclear DNA content was quantified in tumoral cells by microcytophotometric techniques. 106 patients with colo-rectal cancer. Patients with colonic perforation, other concomitant neoplasia, non-curative surgery or receiving adjuvant therapies were excluded from the study. Five patients died during the postoperative period and one was lost. Histological grade: 28% G1, 35% G2 and 37% G3. Dukes': 8% A, 40% B, 32% C and 20% D. DNA quantification has rendered 45% as euploid and 55% as aneuploid. There was no statistical correlation between ploidy and location, age, sex or CEA. However, there is a clear preponderance of euploid tumors in G1 (23 vs. 5), while the aneuploid tumors double the euploid ones (24 and 25 vs. 12 and 12) in G2 and G3. A similar result was found comparing ploidy and Dukes: euploid tumors reach 77% both in stages A and B, while they drop to 24% and 14% in stages C and D. It has also been found that euploid tumors show a longer period of survival free of recurrence. Evidence has been found supporting a prognostic value for tumoral DNA quantification in colo-rectal cancer. A longer follow-up is required to study absolute survival of the patients.