While there are extensive data showing that aneuploidy is associated with adverse outcome in stage D prostate cancer, the utility of ploidy analysis in stage B disease is unclear. We determined ploidy in radical prostatectomy specimens from 28 patients with clinical stage B prostate cancer, and with a mean follow-up of 4.1 years (2-10 years). Patients who had no recurrences had a minimum 5 years of follow-up. Patients who had only 2 years of follow-up were included if they had developed bone metastases during this period. 2. Ploidy determinations were done on Feulgen-stained 5-microns paraffin-embedded sections using a CAS 200 image analyzer. At least 400 tumor cells were counted in every case. Tumors with at least 70% diploid cells were classified as diploid, while those with less than 70% diploid cells were classified as aneuploid. The mean percentage of diploid cells in tumors classified as diploid was 90.6 +/- 7.4, while the mean percentage of diploid cells in tumors classified as aneuploid was 36 +/- 21.9. 3. Ploidy status correlated with disease progression: seven of the 10 patients (70%) with disease recurrence had aneuploid tumors, while 13 of 18 patients (72%) who remained disease-free had diploid tumors (P = 0.03, Chi-square test). 4. These data show that patients with stage B disease with aneuploid tumors at the time of prostatectomy are more likely to have recurrent disease within a mean of 3 years (2-6 years) compared to patients with diploid tumors.(ABSTRACT TRUNCATED AT 250 WORDS)