PURPOSE: It is well known that the clinicopathologic stages of colorectal cancer are correlated to the prognosis of patients and are used to select the method of adjuvant treatment. Many studies suggest that the DNA ploidy pattern is a supplementary prognostic marker. For that reason, we studied the relationships between the DNA ploidy pattern and the incidence, sex, age, tumor location, tumor size, histopathological classification, stage, lymph node, liver, pertioneal metastases and prognosis in patients with colorectal cancer. METHODS: 373 patients with colorectal cancer who had undergone surgical resection at the Hospital between January 1980 and January 2000 were studied. The DNA ploidy pattern was analyzed by FACScan flow cytometry (Becton- Dickinson Immunocytometrical Systems, Mountain View, CA). The relationships between DNA ploidy pattern and various clinicopathologic characteristics were compared retrospectively. RESULTS: Cases of diploidy numbered 167 (44.8%) and aneuploidy 206 (55.2%). The mean size of the tumor mass was larger in the diploidy group. DNA diplody was more frequent in ascending, transverse and descending colon cancers. Aneuploidy was more frequent in sigmoid colon and rectal cancers. In regards to histopathologic classification, mucinous & poorly differentiated adenocarcinomas were inclined to diploidy and well differentiated and moderately differentiated adenocarcinomas were inclined to aneuploidy. Lymph node and liver metastases were more statistically significant in the aneuploidy cases. The DNA ploidy pattern had no significant correlation to age, sex, stage, peritoneal metastasis, or prognosis. CONCLUSION: The DNA ploidy pattern is useful for evaluating the biological behavior of tumors such as tumor growth, tumor location, histopathological differentiation and lymph node metastasis, although it is not useful for determining survival or prognosis.