In 27 patients who underwent partial duodenopancreatectomy due to cancer of the ampulla of Vater, in addition to the TNM classification and usual morphologic criteria, the paraffin-embedded material underwent deparaffinization, was rehydrated, and was mechanically and enzymatically processed into a single-cell solution. For evaluating the DNA histogram this was analyzed with the help of automatic single cell cytophotometric study. At the time of DNA analysis the histomorphological data and the survival time of the patients were not known. In the univariate analysis the 5-year survival rate of patients with diploid or hypotriploid tumors (n = 12) was 69% of patients with diclonal (diploid-triploid n = 7, triploid-tetraploid n = 1) tumors was 62.5% and no patient with a triploid or hypertriploid tumor (n = 7) survived 5 years. No association could be found between the known prognostic criteria and the DNA content. The multivariate analysis shows that beside the lymph node status, the DNA content of tumor cells had a strong and independent influence on the prognosis in cancer of the ampulla of Vater.