As a rate per million kilometres travelled, the 'risk' of cycling appears to be high in relation to other forms of transport. Yet, in absolute numbers, there are far fewer cyclist deaths than pedestrian or motor vehicle occupant deaths, and most deaths and serious injuries to pedal cyclists are caused by other road users--principally motor vehicles. The large majority of pedal cyclist deaths are due to head injuries after collision with a motor vehicle. It is therefore commonly proposed that cyclists should wear crash helmets for their own 'safety'. Helmets may protect against fall injuries, but current models are not designed to withstand the impact of collisions with motor vehicles. Evidence for the benefit of pedal cyclists wearing helmets is limited: the existing studies cannot exclude the possibility of different risk-taking behaviour, either by cyclists or by motor vehicle drivers, for helmet wearers compared with non-wearers. A public health policy towards reducing pedal cyclist deaths should seek prevention of accidents, rather than protection from their consequences. Cycling in greater safety would reduce the 'risk' per kilometre travelled, but more cycling might not reduce total cyclist deaths or injuries--because of greater exposure. The 'risk' of cycling--the risk of injury or death--is a complex mix of exposure, 'danger' of the environment, and the perceived risk affecting our precautionary preventive behaviour.