The overall goal of this study is to characterize the genetic basis for the inherited predisposition to prostate cancer. Our hypothesis is that prostate cancer susceptibility loci can be identified and characterized using a family-based association approach. Our approach, which ascertains men with early-onset and/or hereditary prostate cancer and their unaffected brothers, examines the contribution of common variation in known candidate genes and pathways to prostate cancer susceptibility. Because the incidence of prostate cancer varies widely by race and country of origin, it is possible that unrecognized, genetic differences between affected and unaffected men could contribute to spurious results in an association study. The advantage of our family-based association approach, however, is that the unaffected men are ascertained from the same genetic source population as the affected men, thereby eliminating the possibility of confounding due to population substructure.