This study was part of the Dunedin Multidisciplinary Health and Development Study. This is a longitudinal study of the health, development and behaviour of a cohort of 1037 young people born in Dunedin, New Zealand between 1 April 1972 and 31 March 1973. Explanatory measures covering background, behavioural and personality factors were obtained at ages 15 and 18 and were used as potential predictors of outcomes reported at age 21. Four outcomes were considered: any crash, injury crash, non-injury crash, and serious injury (not motor vehicle related). Overall, very few lifestyle factors were important predictors of any of these outcomes. Factors that were shown to predict injury crashes differed from those that predicted non-injury crashes. Also, those that predicted a traffic crash differed from those that predicted a serious non-traffic injury. These results suggest that focusing injury prevention efforts on changing the lifestyles of young adults is unlikely to reduce overall crash risk, and would have little impact on the risk of serious injury.