To study the association of DNA ploidy abnormality and p53 overexpression with the carcinogenesis of colorectal cancer. Methods: DNA ploidy and p53 expression were measured in a series of 42 colorectal adenocarcinomas by means of flow cytometry and immunohistochemical test. Results: 17 tumors (40%) were diploid and 25 (60%) aneuploid. The aneuploid tumors were significantly more common in the distal colon than in the proximal colon (P<0.01). Aneuploidy was significantly associated with lymph node metastasis (P<0.05). There was no correlation between DNA ploidy and the other clinicopathological variables. Of the 22 samples examined, the positive rate of p53 expression was 59% (13/22). P53 expression was more frequently observed in the distal tumors (11/13) than in the proximal tumors (2/9) (P<0.05). Conclusion: Our data support the hypothesis that the carcinogenesis of colorectal cancer might differ in proximal and distal tumors. DNA ploidy abnormality and p53 overexpression may play an important role in the development of distal colorectal cancer.