Many jurisdictions require cyclists to wear bicycle helmets. The UK is currently not one of these. However, an increasing number of interest groups, including the British Medical Association, want to change the status quo. They argue that mandatory cycle helmet laws will reduce the incidence of head injuries and that this will be both good for cyclists (because they will suffer fewer head injuries) and good for society (because the burden of having to treat cyclists suffering from head injuries will be reduced). In this paper we argue against this position. We suggest that cycle helmets may not be especially effective in reducing head injuries and we suggest that the imposition of such a restrictive law would violate people's freedom and reduce their autonomy. We also argue that those who accept such a restrictive law would be committed to supporting further legislation which would force many other groups - including pedestrians - to take fewer risks with their health. We conclude that cycle helmet legislation should not be enacted in the UK unless, perhaps, it is restricted to children.