Between the prognostic indices in the colorectal cancer the ploidy has determined a great interest. To study the value of ploidy in the prognosis of the colorectal cancer, as a sign of the aggressiveness of the tumor for a therapeutic help, we have examined, in a retrospective study, 150 patients who had a colorectal cancer resected from 1980 to 1986. We have compared ploidy of specimens of paraffin-embedded tumors and Dukes' stage, Grading, the over-all, distal and local recurrence and the survival at 5 years. The statistics were performed by the chi-square test, the Fisher exact-test and the Wilcoxon test. The aneuploids are 126 (84%) and the diploids 24 (16%). The correlations of ploidy and the Duke's stages, the Grading, and the over-all and local recurrence are not statistical significant. The distal recurrence of the aneuploids and the better survival of the diploids are significant. In conclusion the ploidy is only a generic indicator of the aggressiveness of the tumor, not useful for a more complete therapeutic choice.