During the 1980s, a sustained campaign increased the rates of helmet use of Victorian bicyclists. The efficacy of helmet use was evaluated by comparison of crashes and injuries (AIS-1985) in 366 helmeted (261 Australian Standard approved and 105 non-approved) and 1344 unhelmeted casualties treated from 1987 through 1989 at Melbourne and Geelong hospitals or dying before hospitalization. Head injury (HI) occurred in 21.1% of wearers of approved helmets and in 34.8% of non-wearers (p < 0.001). The AIS scores were decreased for wearers of approved helmets (p < 0.001), face injuries were reduced (p < 0.01), and extremity/pelvic girdle injuries increased (p < 0.001) and the overall risk of HI was reduced by at least 39% and face injury by 28%. When casualties with dislodged helmets were excluded, HI was reduced 45% by approved helmets. Head injury reduction by helmets, although substantial, was less than that found in a similar study in Seattle, Washington.