Eighty-six specimens from 25 patients with Barrett's epithelium were analyzed by both histology and flow cytometry. Of these, 73 were without dysplasia and 13 had dysplasia (7 low grade, 6 high grade). Eight of the nondysplastic specimens were aneuploid and another 15 had increased G2. Among the dysplastic specimens, two were aneuploid and two had increased G2. These data were grouped into four classifications: type 1 (65 specimens), specialized columnar epithelium (Barrett's) without dysplasia and no aneuploidy; type 2 (8 specimens), Barrett's epithelium without dysplasia and an aneuploid cell population; type 3 (11 specimens), Barrett's epithelium with dysplasia and no aneuploidy; and type 4 (2 specimens), Barrett's epithelium with dysplasia and aneuploidy. Distribution by type was 76%, 9%, 13%, and 2%, respectively. We conclude that histologic dysplasia and aneuploidy are often discordant. They may identify separate subgroups at risk, or when concordant, may reflect an increased cancer risk in that population. Further study will define the role of histology and flow cytometry in the screening and management of patients with Barrett's esophagus.