We conducted a genomewide screen for prostate cancer-susceptibility genes on the basis of data from 98 families from the United States and Canada that had three or more verified diagnoses of prostate cancer among first- and second-degree relatives. We found a statistically significant excess of markers for which affected relatives exhibited modest amounts of excess allele-sharing; however, no single chromosomal region contained markers with excess allele-sharing of sufficient magnitude to indicate unequivocal evidence of linkage. Positive linkage signals of nominal statistical significance were found in two regions (5p-q and 12p) that have been identified as weakly positive in other data sets and in region 19p, which has not been identified previously. All these signals were considerably stronger for analyses restricted to families with mean age at onset below the median than for analyses of families with mean age at onset above the median. The data provided little support for any of the putative prostate cancer-susceptibility genes identified in other linkage studies.