Previous studies have demonstrated that booster seats reduce the risk of seat belt syndrome, in particular the occurrence of abdominal organ injuries, by improving the fit of the seat belt on young children and encouraging better posture and compatibility with the vehicle seat itself. However, other researchers have shown that abdominal injuries are still prevalent even with the use of booster seats. In the US, as booster seat use increases and more data become available, particularly on older children in booster seats, the abdominal injury risk to these children should be revisited. Therefore the objective of this study was to quantify the time trend increase in appropriate restraint for rear row(s) seated children age 4 to 7 years old and define the prevalence of abdominal injuries in those restrained by beltpositioning booster seats. A probability sample of 4,517 crashes involving 5,259 children, weighted to represent 89,588 children in 77,153 crashes was collected from an on-going child specific crash surveillance system between December 1, 1998, and December 31, 2005. Appropriate restraint, including the use of belt positioning boosters, increased from 17% to 67% among 4 to 7 year olds during the time period of data collection. In frontal impacts, abdominal injuries occurred among 0.25% of all 4- to 7-year-olds, including 0.32% of those in seat belts and 0.04% of those in belt-positioning booster seats. Among children restrained in belt positioning booster seats, we were not able to detect a difference in the risk of abdominal injuries between the age groups This study, conducted on a dataset with increased booster use by 6 and 7 year olds, confirms previous analyses that point to a reduced abdominal injury risk for children in belt-positioning booster seats. Abdominal injuries still occurred in some boosterseated children, however, suggesting the need for further in-depth study into the circumstances surrounding these injuries.