Abstract In September 2011 the Belgian Road Safety Institute (BRSI) conducted its first roadside survey of child restraint system (CRS) use and misuse. The aim of this study was to obtain population-bases estimates of the prevalence of use and misuse of CRS and to identify predictors of misuse on the basis of observations in real traffic conditions. The survey was conducted on randomly selected sites across the country, stratified across various types of journeys. The principal parameters analysed were: the characteristics of the children and the car drivers, type of journey, types of CRS and types of misuse. The sample consisted of 1461 children (under 135cm) for whom the conditions of restraint were observed in detail and the driver was interviewed. At least 50% of the children were not correctly restrained and 10% were not restrained at all. The most significant factors associated with CRS use were the use of a seatbelt by the driver (31% of unrestrained children for unbelted drivers, compared to 7% for belted drivers - only 32% of correctly restrained children for unbelted drivers compared to 54% for belted drivers), whether the CRS was bought in a specialized shop (only 27% of misuse compared to 45% of misuse for CRS both in supermarkets) and the age of the children. The proportion of correctly restrained children (appropriate without misuse, the bottom category in the figure) has a roughly curvilinear relation with age; decreasing from 75% at age 0 to 24% at age 8 and going back up to 63% at age 10. Although the sample of ISOFIX users was small (n =76), it appears that the ISOFIX system reduced misuse significantly. Most of the drivers were ignorant of their own errors concerning the inappropriateness and/or misuse of the CRS or they were remiss and underestimated the risk. The three main reasons given by the drivers to explain or justify the misuse noticed were: low attention level to safety (inattention, time pressure, and short distance), the child's resistance to be restrained, children restraining themselves and problems with the CRS. The present results suggest little or no change in the level of correct CRS use over the last five years and clearly reveal the unacceptably high levels of incorrect and/or inappropriate CRS use. This calls for campaigns and other actions to inform and motivate the population.