In a family with a constitutional translocation t(3;6), the oldest member carrying the translocation had developed multiple nonpapillary renal cell carcinomas (RCCs). The translocation breakpoint was positioned between 3p13 and 3p14.1. This is close to the region in which a t(3;8) breakpoint has been reported in a family with hereditary RCC. We defined the location of the t(3;6) and t(3;8) breakpoints by fluorescence in situ hybridization (FISH) analysis with yeast artificial chromosomes (YACs) from the 3p14-13 region. Both interphase nuclei and metaphase cells from translocation-carrying members of both families have been used, allowing the definition of flanking YACs for each breakpoint. We could thereby clearly confirm that the breakpoints are different, the t(3;8) breakpoint being most distal. In addition, we have shown that both translocation breakpoints are located distal to the homozygously deleted region in the U2020 lung cancer cell line.