Polyps with epithelial dysplasia in ulcerative colitis (UC) represent either dysplasia-associated lesions or masses (DALMs) or sporadic adenomas. DALMs are frequently associated with associated carcinoma and are an indication for colectomy. Removal of the polyp is treatment of choice for sporadic adenomas. Differentiating between these 2 lesions is not always easy. The goal of this study was to distinguish DALMs from adenomas in patients with UC on a genetic basis. We evaluated genetic alterations in DALMs and compared them with a previously published set of dysplastic polyps in patients with UC that were considered adenomas for the following reasons: (1) polyps were located outside of current active disease; (2) polyps had histological features of sporadic adenomas; and (3) patients displayed a uneventful follow-up after polypectomy (UC-adenomas). In addition, adenomas not associated with UC were studied. Genetic alterations on chromosome 3p were assessed for the markers D3S1766, D3S2409, and D3S2387. LOH with or without microsatellite instability was found in 70%, 37%, and 57% of cases of DALM, respectively. In contrast, UC-adenomas lesions exhibited genetic alterations in 8.3%, 11.7%, and 15.3% for the respective markers. Spontaneous adenomas exhibited genetic alterations in 10.5%, 7.1%, and 0% of cases, which were not significantly different from the UC-adenoma results. These results indicate that UC-adenomas are genetically and biologically similar to sporadic adenomas and that UC-adenomas may biologically represent sporadic adenomas, supporting on a genetic basis the criteria chosen to diagnose adenomas in UC. Genetic markers on chromosome 3p may be useful in the differential diagnosis between DALM and UC-adenomas.