Benign prostatic hyperplasia (BPH) and prostate cancer are conditions commonly affecting the prostate gland in aging men. Prior epidemiological studies investigating potential associations between the two have resulted in conflicting data. Recent morphological studies have demonstrated the occurrence of a subset of prostate cancers as arising in the transition zone of the gland, the same region where BPH occurs. A morphologic lesion, atypical adenomatous hyperplasia (AAH), providing a possible link between cancer and BPH has been described. Biological studies of this potential precursor lesion are not yet available, but will be essential in order to further investigate this possible association.