DNA content of prostatic adenocarcinoma was determined by flow cytometry on formalin-fixed, paraffin-embedded tissue from 57 radical prostatectomies. This was done to define the relationship of aneuploidy to prostatic adenocarcinoma grade, volume, and pathologic stage and to examine its utility in candidates for surgical treatment. Aneuploidy was found in 26 (46%) cases. With one exception, all of the aneuploid cases were found in tumors larger than 4 cc. The percentage of aneuploid cases increased with advancing pathologic stage, and it was highest in those cases with lymph node metastases. This percentage was also higher among more poorly differentiated tumors. However, diploid tumors were also found among these groups, and the relationship between aneuploidy versus pathologic stage and grade did not achieve statistical significance. Except for a 91% specificity for tumor volume greater than 4 cc, the sensitivity and specificity of DNA content analysis to predict these groups was low (50% to 72%). It is concluded that aneuploidy is a later event linked to tumor progression, but it is not a requirement for progression to occur. The overlap in aneuploid and diploid tumor behavior precludes the use of DNA content analysis as an independent predictor to direct preoperative treatment of prostatic carcinoma.