Prostate cancer (PRCA) is the most common cancer diagnosed (1999 estimate 179,300 cases) and the second leading cause of cancer mortality (1999 estimate 37,000 deaths) in men in the United States. Family history is the single strongest risk factor currently known for prostate cancer. This raises the possibility that heritable genetic factors may be involved in the development of this disease in a subset of men. The genetic contribution to diseases of complex origin such as cancer is often most salient in families of early onset cases. Therefore, prostate cancer inheritance following a simple Mendelian pattern may be identified in the families of probands with early-onset cases. Common susceptibility alleles of small effect may be detectable in families with later-onsent and/or less strong family history of PRCA or in case-control data.