Metastatic malignant disease is the single most common cause of treatment failure and subsequent mortality of most human malignancies, including prostate cancer. Presently, cells expressing the metastatic phenotype cannot be identified within a primary tumor population. Hence, accurate assessment of the likely behavior of an individual primary malignancy cannot be made at the time of diagnosis. The studies now reported have been aimed at identifying some of the features that may be associated with the metastatic phenotype of prostatic cancer. Insight into those factors that may be involved in prostate cancer metastasis has been gained from a variety of experimental approaches as well as study of intact human prostate cancers.