Prenatal diagnosis (PND) and preimplantation genetic diagnosis (PGD) for later onset and/or reduced penetrance inherited cancer predispositions, e.g. familial adenomatous polyposis, hereditary non-polyposis colorectal cancer/Lynch syndrome and hereditary breast and ovarian cancer, raise a number of ethical issues. Some of these are the same as for conditions which present early in childhood, are fully penetrant and for which no/limited treatment options are possible; others relate to whether reduced penetrance and/or the availability of treatment mean that these are not serious (enough) conditions to warrant tests prior to/during pregnancy or to justify termination of pregnancy. However, attempts to reach a consensus on what counts as a serious (enough) condition in the context of PND and PGD have been unsuccessful. Such a definition may anyway be unhelpful if it cannot also take into account, for example, the woman’s/couple’s awareness and experience of the condition and the impact of the condition on affected individuals and their families. Individuals affected by, or at high risk of, later onset and/or reduced penetrance inherited cancer predispositions are generally supportive of access to PND and PGD for their own conditions, even if they would not consider using it themselves. Professionals working in clinical cancer genetics need to be prepared to discuss PND and PGD with this group of patients.