Until the 1980s, the study of the genetics of cancer was confined to the rarer familial cancer syndromes, such as multiple endocrine neoplasia type 2 and familial polyposis coli. This was restricted to a relatively small number of families. With the advent of the knowledge that at least a small proportion of many of the common cancers is due to an inherited genetic predisposition, the overall numbers of individuals at risk will be large because these cancers are more common. For example, it has been estimated that about 5-10 per cent of breast cancers may occur as a result of the inheritance of a dominant gene.1 This would equate to 1250 cases of breast cancer per year in the UK occurring in susceptible individuals. This led to the development of cancer family clinics, specializing in the management of families at risk of hereditary cancers.