Human prostate gland is a composite organ made up of several glandular and nonglandular components. There are three distinct glandular regions. These are the peripheral, the central, and the transition zone. They differ histologically and biologically. The central zone is relatively resistant to carcinoma and other diseases. The peripheral zone is the site of origin of most carcinomas and prostatic intraepithelial neoplasia (PIN). Most authors now agree that PIN is a likely precursor of at least a proportion of carcinomas arising in this zone. The transition zone is the exclusive site of origin of benign prostatic hyperplasia (BPH). A subset of prostate cancers arises in this zone as well. Most are found incidentally at transuretral resection (TUR). A morphological lesion, atypical adenomatous hyperplasia (AH), arising also in transition zone, provides a possible link between BPH and transition zone cancers. However, further studies of biological markers of neoplastic transformation are needed to address this issue.