Prognostic factors in transitional cell carcinoma of the upper urinary tract were assessed with histopathological examination and flow cytometric analysis in a series of 127 patients operated upon between 1976 and 1988. In particular, we evaluated the usefulness of flow cytometry to identify patients who require adjuvant treatment among those with low grade and low stage disease (51% in this series). A multivariate analysis was done on 92 cases, considering patient age and sex, stage, grade and number of lesions (unifocal versus multifocal), site (renal pelvis versus ureter), presence of vesical tumors, recurrences along the urinary tract or in the bladder, type of operation and nuclear deoxyribonucleic acid (DNA) ploidy (diploid versus tetraploid/aneuploid tumors). Only the stage (p = 0.001), grade (p = 0.001) and, to a lesser extent, the DNA pattern (p = 0.031), as well as the number of lesions (p = 0.061) were determinant for prognosis. In regard to the subgroup of 41 patients with grade 2 or less, stage P1 or less tumors, no significant difference in survival was demonstrated between diploid and nondiploid tumor patients. However, 7 of 10 patients from the latter group are still under observation. Therefore, our conclusions may have to be modified in the future.