The CAG repeat in exon 1 of the androgen receptor (AR) genes has been postulated as both a susceptibility allele and phenotypic modifier in BRCA1-associated breast cancers. We have analysed this repeat in a set of 178 breast cancer cases who have been selected only for age of presentation at 65 years or less. No effect of repeat length on age of presentation was found and there was no association between repeat length and family history. In combination with the data from other workers, our findings suggest that the androgen receptor repeat does not act as a modifier gene or susceptibility locus outside the context of the hereditary breast/ovarian cancer syndrome.