This chapter reviews the genetic basis of prostate cancer, and concentrates on inherited predisposition to prostate cancer as the hereditary component of prostate cancer is believed to be the largest of all tumor types. No differences were found in the three groups divided on the basis of the degree of hereditary prostate cancer characteristics being present in the family. The first group consisted of men who were considered as having a hereditary form of the disease: 3 or more affected in a single generation, prostate cancer occurred in three successive generations, or two cases of prostate cancer diagnosed before the age of 55. The second and third groups consisted of individuals with either no affected family members, or family members were affected, but not to the degree as in the first group. The elucidation of the real nature of these associations awaits the identification of the prostate susceptibility genes.