Flow cytometric DNA ploidy of colorectal adenomas resected from 34 patients and the corresponding patient family history in first-degree relatives were evaluated. The samples with at least two separate G0-G1 peaks were defined as DNA aneuploid. The correlation between DNA ploidy and family history was evaluated using two-by-two contingency tables. This correlation was highly statistically significant: seven of nine patients (78%) with positive family histories, and five of 25 (20%) with negative family history had adenomas with DNA aneuploid stemlines (P = 0.0068). The overall DNA aneuploidy incidence was 12 in 34 cases (35.2%). The combined information of DNA aneuploidy and positive family history of colorectal cancer in patients with colorectal adenomas may help to better understand the process of colon carcinogenesis and to identify patients who have a higher risk for developing a malignancy.