['The American Academy of Pediatrics has established guidelines for optimal, age-appropriate child occupant restraint. While optimal restraint has been shown to reduce the risk of injuries overall, its effect on specific types of injuries, in particular abdominal injuries, has not been demonstrated.', 'Cross-sectional study of children aged younger than 16 years in crashes of insured vehicles in 15 states, with data collected via insurance claims records and a telephone survey. A probability sample of 10927 crashes involving 17132 restrained children, representing 210926 children in 136734 crashes was collected between December 1, 1998 and May 31, 2002. Restraint use was categorized as optimal or suboptimal based on current American Academy of Pediatrics guidelines. The outcome of interest, abdominal injury, was defined as any reported injury to an intra-abdominal organ of Abbreviated Injury Scale >or=2 severity.', 'Among all restrained children, optimal was noted in 59% (n = 120473) and suboptimal in 41% (n = 83555). An associated abdominal organ injury was noted in 0.05% (n = 62) of the optimal restrained group and 0.17% (n = 140) of the suboptimal group. After adjusting for age and seating position (front vs. rear), optimally restrained children were more than 3 times less likely [odds ratio 3.51 (95% confidence interval, 1.87-6.60, P < 0.001)] as suboptimally restrained children to suffer an abdominal injury. Of note, there were no abdominal injuries reported among optimally restrained 4- to 8-year-olds.'] Does optimal restraint reduce the risk of abdominal injury in children involved in motor vehicle crashes?