The practice of genetic counselling gives rise to many ethical dilemmas, and counsellors need to be familiar with the principles of biomedical ethics. The primary principles include respect for autonomy, beneficence, non-maleficence and justice. A case of identical twins at 50% risk for Huntington's disease, in which only one twin sought predictive testing for this dominantly inherited disease, created several ethical dilemmas. Another case where predictive testing was carried out on two young children, at high risk, by a laboratory at the request of an adoption agency and a doctor, with a view to giving information to the foster parents, also posed many ethical conundrums for the counsellor. The ethical issues that arose in these cases are discussed in this paper.