Recent research makes it probable that there is a hereditary form of prostate cancer. By identifying prostate cancer cases in the Swedish twin registry it was possible to show a pronounced difference in proband concordance rates and correlation of liability between monozygotic and dizygotic twin pairs, which indicates strongly that genetic factors are important for prostate cancer. In a nation-wide register cohort study it was found that the risk for prostate cancer was approximately two times higher among sons to prostate cancer patients when compared to Swedish men in general. By linkage analyses at least two loci for putative prostate cancer genes have been identified, one on chromosome 1 (1q24-25) and one on the X-chromosome (Xq27-28). Before genetic testing becomes available it was suggested that men with the familiar aggregation of prostate cancer should be evaluated with a PSA test on a regular basis.