In 1970 the Government of the State of Victoria became the first in the 'western' world to introduce legislation for compulsory wearing of seat belts. Within 14 months the other Australian states followed. Seat belt wearing rates increased to attain 90 per cent in 1977. This paper presents an evaluation of changes during the period 1955--77 in the incidence of road crash fatalities and injuries for vehicle occupants in Victoria and the rest of Australia. The introduction of the legislation in Victoria and subsequently in the other Australian states coincided with significant and marked decreases in driver and passenger fatality and injury rates (numbers per 10 000 registered vehicles). The decreases were enough to reduce the total numbers of vehicle occupant fatalities and injuries for all post-legislation years in Victoria. The improvements have been maintained throughout the entire post-legislation period. The legislation did not apply to child passengers of less than 8 years of age and the frequency of seat belt or harness wearing among them remained low. These children did not share in the overall improvement for passengers. The Australian experience supports the view that legislation for compulsory wearing of seat belts is the single most effective method available for the protection of vehicle occupants in road crashes.