Drawing on provincial data files maintained by Transport Canada, the injury experience of passenger vehicle occupants as a function of occupant seating position, reported restraint use and occupant age is examined. Particular attention is given to the issue of rear seat lap belt effectiveness. Estimates of restraint system effectiveness are derived using a variety of approaches. These range from direct comparisons of the relative injury/fatality rates of restrained and unrestrained occupants in reportable accidents to double-pair comparisons based on “subject” and “control” occupants in fatal accidents.Available Canadian data suggest that the use of three-point seat belts by front seated occupants and the use of lap belts by rear seated occupants substantially reduces the likelihood of serious or fatal injury. The likelihood of serious injury or death among front seated occupants is reduced by 40%-55% through the use of a three-point seat belt, and among rear seated occupants by 20-50% through the use of a lap belt. Three-point seat belts were observed to be slightly more effective in frontal impacts than in non-frontal impacts. The situation is reversed in the case of lap belts. The degree to which the effectiveness estimates may be exaggerated either by exposure differences between restrained and unrestrained occupants or by inaccuracies in police-reported restraint use is discussed.