BACKGROUND: To search for and quantify the importance of socio-economic inequality in seat belt use in young Belgians (15-24 years old). METHODS: Using the data of the National Health Survey of Belgium (1997), socio-economic indicators were constructed combining characteristics of the individual and the household to which s/he 'belongs' (equivalent household income, employment, poverty, subjective poverty, and socio-economic insecurity) and the corresponding concentration curves and indices were calculated. RESULTS: Significant differences were found in seat belt use related to young people's socio-economic status. The failure to buckle up was concentrated most heavily in the least favoured socio-economic groups. Such inequality was a constant finding, although its magnitude varied according to the socio-economic indicator used, going from -0.142 for the variable 'occupational category of the household' to -0.028 for the variable 'poverty'. CONCLUSIONS: This finding of true socio-economic inequality in the use of seat belts by 15-24 year olds should prompt special vigilance in health promotion approaches aimed at changing behaviour. It also underlines the importance of being attentive to the socio-economic indicators that are chosen to quantify such inequality in intra- and inter-country comparisons. ; Journal Article ; Research Support, Non-U.S. Gov't ; SCOPUS: ar.j ; info:eu-repo/semantics/published