This review examines selected areas of contemporary prostate cancer research in terms of the impact of prostatic cellular and histopathological heterogeneity. Prostate tumor progression is accompanied by dysregulation of multiple growth factor networks as well as disruption of normal patterns of cell-cell interactions. Molecular and cytogenetic studies demonstrate that prostate cancer results from the accumulation of several different genetic defects. No single event predominates, but modifications in tumor suppressor genes or functional elimination of the suppressor gene product are more common than activation of known oncogenes. Intratumor heterogeneity is also detectable at the genetic level. This further complicates efforts to correlate modifications at specific loci with progression or outcome. The development of new in vitro and in vivo systems for the study of human prostate cancer should increase our understanding of this complex disease. In each approach, knowledge of the histopathology of the normal and neoplastic prostate is essential.