In order to design injury-preventive programmes aimed at parents, an understanding of injury-preventive behaviour is essential. Questionnaires were obtained from 870 mothers of 3, 4 and 9-year-olds. The perceived social norm and other determinants for injury-preventive behaviour were analysed using three multivariate logistic regression models. The final logistic models classified 73.2-82.7% of respondents correctly. Perceived norms of relatives and friends were found to be the most important determinants of mothers' injury-preventive behaviour. Injury-preventive behaviour could neither be explained by mother's perception of injury risks, nor by the perceived norms of professionals within child health care and schools. This study indicates that in order to design injury-prevention programmes, an understanding of social norms is crucial.