http://www.cyclehelmets.org/1012.html

Most fatalities involve multiple injuries and head injury is not the sole cause of death. The experience of a solicitor specialising in cyclist injuries (BHRF, 1173) supports the view that deaths solely due to head injury are unusual. Furthermore, fatal head injuries typically involve rotational forces, which cycle helmets do not mitigate and may even make more likely (BHRF, 1039). Cyclist deaths were also investigated in Auckland, New Zealand (Sage, Cairns, Koelmeyer and Smeeton, 1985). 16 of 19 non-helmeted cyclists died from mulitple injuries, so helmets would not have changed the outcome. Only one cyclist died of head injuries in a bike-only crash, the most likely situation for a helmet to help. That cyclist died despite wearing a helmet and a fall at moderate speed. The researchers concluded: "This study indicates that the compulsory wearing of suitable safety helmets by cyclists is unlikely to lead to a great reduction in fatal injuries, despite their enthusiastic advocacy".

A study of cyclist crashes in Brisbane, Australia concluded that helmets would prevent very few fatalities (Corner, Whitney, O'Rourke and Morgan, 1987). All deaths were caused through collisions between a bicycle and a motor vehicle. For 13 of the 14 cyclists who died, there was no indication that a helmet might have made any difference.