The aim of this review study is to compile and analyse the state of knowledge regarding the effects of measures, both legislative and noncompulsory, taken to increase the use of cycle helmets. The results are based mainly on studies from 1990-2002 found in literature databases. The overall conclusion is that a considerable increase in helmet use by cyclists could be achieved by noncompulsory measures, but the use levels are not as high as those achieved by legislation. Most of the positive effects of noncompulsory measures are due to multistrategy programmes at municipal and regional level, where the programmes mostly comprise informational and educational activities in combination with discounts on helmets or reward systems. There is however great variation in the level of helmet use that has been achieved; the observed helmet use which most of the measures achieve seldom exceed 50 % for children/young people and ca 25-30 % for adult cyclists. However, cycle helmet laws in combination with informational and educational activities leads to significantly higher helmet use compared to noncompulsory measures alone. Helmet use often reach 80-90 % on average. Several studies show that helmet laws reduce head injuries among bicyclists. In Australia, for instance, number of fatalities among cyclists decreased by 45 % in average two years after their helmet laws compared to two years before. The effect of cycle helmet laws on cycling is much debated, but results from studies are not unambiguous. Several studies, however, indicates that a cycle helmet law may result in a reduction in cycling by young people and in a certain, but temporary, reduction in cycling by younger children. On the other hand, cycling by adults is probably not influenced.