Organ transplant recipients and other immunodeficient individuals are at risk for the development of Epstein-Barr virus-related B-cell lymphomas. The incidence of lymphoma after cardiac transplantation ranges from 2 to 11%. To determine whether the clinical presentation, histological subtype, or clinical outcome correlated with DNA content, 17 patients with postcardiac transplant lymphoma were studied by flow and image cytometry. Their mean age was 52 yr (range: 33 to 67 yr) with a mean interval of 10 mo (range: 0.5 to 50 mo) between the time of transplantation and the diagnosis of lymphoma. Of the 17 specimens analyzed by flow cytometry, 14 (82%) were diploid and 3 (18%) aneuploid. By image cytometry, 15 (88%) were diploid and 2 (12%) aneuploid. Agreement between flow cytometry and image cytometry was 94%. No statistically significant correlation between DNA content (ploidy and % S-phase fraction) and the interval since transplantation, histological subtype, or clinical outcome could be determined. A rate of DNA aneuploidy was seen that was lower than previously reported for lymphomas with the same histological grade and cell proliferation rate occurring in immunocompetent individuals. These findings are similar to those reported for AIDS-related lymphomas.