Genetic testing is traditionally preceded by counselling to discuss its advantages and disadvantages with individuals so they can make informed decisions. The new technique of whole genome or exome sequencing, which is currently only used in research settings, can identify many gene mutations, including substantial numbers of mutations with unknown pathological effect; it may, therefore, threaten this balanced approach if it is used in a clinical setting. We discuss the ethical challenges of several approaches to pre- and postnatal DNA testing, individual privacy versus the interests of families and of scientists, and the clinician's duty to re-contact if new information or options become available.