Objective: To evaluate the relationship between flow cytometric DNA ploidy, biological features and prognosis in patients with Stage II colorectal cancer. Methods: Nuclear DNA content, proliferation index and S-phase fraction were measured in a prospective series of 45 patients with curatively resected Stage II colorectal adenocarcinomas by means of flow cytometry using frozen tumor samples. Results: Of the 45 samples examined, 17 tumors (38%) were diploid and 28 (62%) aneuploid. The diploid tumors were significantly more common in the proximal colon than in the distal colon (67% vs. 23%; P<0.01). There was no correlation between DNA ploidy and the other clinicopathological variables (P>0.05). The proliferation index and S-phase fraction in the distal tumors were higher than those in the proximal tumors, but the difference was not significant (P>0.05). When the 5-year survival rate of patients with Stage II colorectal cancer was compared by the log rank test, a significant relationship between DNA ploidy status and disease free survival was observed in the group of all patients. Patients with DNA diploid tumors had a better disease free survival than those with DNA aneuploid tumors (P<0.05). Conclusion: These findings support that DNA ploidy status, proliferation index and S-phase fraction may differ in the proximal and distal colorectal cancer. Flow cytometric DNA ploidy status might be a useful prognostic factor in patients with Stage II colorectal cancer. Objective: To evaluate the relationship between flow cytometric DNA ploidy, biological features and prognosis in patients with Stage II colorectal cancer. Methods: Nuclear DNA content, proliferation index and S-phase fraction measured measured a series of 45 patients with curatively resected Stage Results: Of the 45 samples examined, 17 tumors (38%) were diploid and 28 (62%) aneuploid. The diploid tumors were significantly more common in the proximal colon than The distal colon (67% vs. 23%; P<0.01). There was no correlation between DNA ploidy and the other clinicopathological variables (P>0.05). The proliferation index and S-phase fraction in the distal tumors were higher than those In the proximal tumors, but the difference was not significant (P>0.05). When the 5-year survival rate of patients with Stage II colorectal cancer was compared by the log rank test, a significant relationshi p between DNA ploidy status and disease free survival was observed in the group of all patients. Patients with DNA diploid tumors had a better disease free survival than those with DNA aneuploid tumors (P<0.05). Conclusion: These findings support DNA ploidy status , diffusion index and S-phase fraction may differ in the proximal and distal colorectal cancer. Flow cytometric DNA ploidy status might be a useful prognostic factor in patients with Stage II colorectal cancer.