PURPOSE:To examine the prevalence of DNA aneuploidy as a function of the extent of ulcerative colitis and to study the correlation of aneuploidy with clinical characteristics. Furthermore, the occurrence of aneuploidy and dysplasia during colonoscopic surveillance was studied in a subset of these patients.METHODS:By analyzing 5404 biopsy samples of 368 patients with ulcerative colitis, we have evaluated the importance of DNA ploidy measured by flow cytometry. We have also investigated the influence of extent (219 patients with extensive or total colitisvs.149 patients with localized colitis) and duration of colitis on the development of dysplasia (patients with biopsy specimens that showed inflammation alone were compared with those with biopsy specimens that were equivocal or positive for dysplasia) and aneuploidy. Included was a subgroup of patients with ulcerative colitis and primary sclerosing cholangitis (n=16).RESULTS:Aneuploidy was found in 8.7 percent (32/368) of all patients. The prevalence of aneuploidy increased by the extent of ulcerative colitis (2 percent localized, 6.8 percent extensive colitis, 14.9 percent total colitis). The frequency of aneuploidy was higher in patients with disease duration longer than 10 years (P=0.007). Patients with ulcerative colitis and primary sclerosing cholangitis were more likely to develop aneuploidy (9/16, 56.3 percentvs.14/120, 11.7 percent;P<0.001) and dysplasia (4/16, 25 percentvs.10/120, 8.3 percent;P=0.06) than patients without primary sclerosing cholangitis.CONCLUSION:Because DNA aneuploidy represents an early alteration during neoplastic transformation in ulcerative colitis, flow cytometry is a valuable tool in the surveillance of those patients. Primary sclerosing cholangitis represents an additional risk factor for the development of DNA aneuploidy and dysplasia.