Advances in human genetics will soon allow prenatal diagnosis of genetic conditions in the fetus that range from trivial to devastating. This commentary explores the concept of severity in genetic diseases and decisions regarding selective abortion. Familial Alzheimer disease is used as a model for the analysis of ethical issues raised by prenatal diagnosis and the subsequent termination of pregnancy. The genetics of the disease has yet to be elucidated, but this condition may be amenable to prenatal diagnosis in the near future, at least in some families. Abortion is a choice open to women in the United States; however, it is still desirable to discuss on purely ethical grounds pregnancy termination in the case of late-onset but severe diseases.