The recent advances in molecular genetics have uncovered new ethical dilemmas in cancer genetics as vexed and almost certainly more complex as in the disease which has provoked the most debate; Huntington disease. Many genes that predispose to cancer have no effect until well into adult life and, as with Huntington disease, important issues arise about predictive tests in fetal, childhood and adult life. Unlike Huntington disease, there are sometimes options that may prevent or at least alter the course to the end result (cancer). Nonetheless, there are hereditary cancers where little or no effective screening or treatment is possible, even when presymptomatic testing shows an individual to carry a cancerpredisposing gene. Many of the lessons that have been learnt from study of Huntington disease can be applied to predictive testing for cancer predisposition genes.1