On July 1, 1990 a law requiring wearing of an approved safety helmet by all bicyclists (unless exempted) came into effect in Victoria, Australia. Some of the more important steps which paved the way for this important initiative (believed to be the first statewide legislation of its type in the world) are described and its effects are analysed. There was an immediate large increase in helmet wearing rates, although teenagers continued to show lower rates than younger children and adults. Considerable reductions in the number of bicyclists killed or admitted to hospital after sustaining head injuries were found in the first year of the law. Analysis of the injury data also showed smaller reductions in the number of bicyclists killed or admitted to hospital who did not sustain head injuries. Limited surveys indicated a considerable reduction in bicycle use by children since introduction of the law.