In this study, over 1000 women with breast cancer were contacted by questionnaire and 164 families with a strong history of breast cancer were identified. Home visits to obtain full pedigree details took place for 123 women, and members of 24 families gave venous blood samples. The extracted DNA was typed by polymerase chain reaction amplification and the derived haplotypes submitted to linkage analysis which confirmed that in 12 families breast cancer susceptibility could be traced to BRCA1. The study demonstrates the number of women at risk of breast cancer in the population, illustrates the complexity of genetic analysis for hereditary breast cancer and demonstrates the problems of predictive analysis in clinical management.