DNA content in paraffin-embedded tissue from 25 normal prostates (NP), 49 specimens of benign prostatic hyperplasia (BPH), 37 specimens of prostatic intraepithelial neoplasia (PIN) and 22 prostatic adenocarcinomas was measured by static image cytometry. During an eight-year follow-up, 47% (23/49) of the males with BPH and 38% (14/37) of the males with PIN subsequently had histologically confirmed prostatic adenocarcinoma, of which 22 cases were analyzed. In 32% of the NPs, 1-3 of 200 measured cells were aneuploid. The mean age of males with aneuploid cells was 55.8 years; it was 33 years for those with only diploid cells (P = .03). In hyperplastic prostatic lesions the percentage of aneuploid specimens increased with the increasing frequency of histologic atypia and with a subsequent malignant outcome. Agreement between the primary benign and later malignant specimen regarding diploidy versus nondiploidy occurred in 17 of 22 patients (77%).