Should people be required to know information about themselves that arises from their genetic test? This question is highly relevant given the NHS's plans to sequence 100,000 whole genomes before 2017. The approach to this issue in the USA generated significant opposition to requiring knowledge, on the basis that it interferes with autonomy. This piece presents a different perspective, arguing that requiring knowledge may not undermine the legal conception of autonomy, giving reason to doubt that it would be unlawful to require people to have genetic information about themselves. Following this, the piece presents an alternative principled position that might support a legal recognition of the interest in not having information about oneself; namely that of preventing personal harm. However, this approach runs into difficulties if the reasons for requiring knowledge are also based on preventing personal harm. The argument considers how interests might be balanced in this competing harms context.