Flow cytometry and image analysis are complementary quantitative cytologic techniques that have demonstrated utility in the assessment and analysis of prostate cancer and other urologic and nonurologic tumors. This review is intended to assess the current state of the art and to project future directions and applications of these modalities in the pathologic assessment of prostate cancer. Special attention is directed toward the topics of prostate cancer detection and diagnosis, determination of patient prognosis, and the monitoring of patient response to therapy. We recommend that 1) flow cytometry and image analysis be used to determine pathologic parameters that will help in predicting poor patient prognosis and 2) quantitative cytologic determinations of DNA content be included in clinical trials so that their ultimate role in monitoring patient response to therapy can be determined. This knowledge will allow the development of protocols designed to test the value of earlier institution of multimodal therapy in high-risk populations.