Heterozygous somatic mutations of the transcription factor, GATA-3, have recently been reported in approximately 5% breast of tumors unselected for family history. We sequenced the GATA-3 gene in 55 breast tumors from women with familial breast cancer, and found seven heterozygous somatic mutations, all in non-BRCA1/2 cases in which the frequency was 22%. In contrast, we found mutations of GATA-3 in only 4% of 81 sporadic tumors analysed. It is possible that GATA3 mutations occur earlier in the evolution of BRCAx tumors, compared to BRCA1, BRCA2 or sporadic tumors, and are therefore easier to detect by direct sequencing in the presence of some stromal contamination.