Background: Motor vehicle crashes represent a significant cause of mortality and morbidity for young children. Safely restraining a child is typically more complicated for special cases such as children treated with a hip spica cast. In the current study, hip spica casts typical for treatment of a femoral fracture were applied to a crash dummy representing the size and weight of a 1-year-old child. This spica casted dummy was used to study the performance of 4 rear-facing car seats in a series of simulated frontal impacts. Methods: The restrained, rear-facing dummy was subjected to a frontal crash test at 30 mph (48 kph) per federal guidelines. Two of the tested car seats were specifically designed for transporting children with hip spica casts, while the other 2 were conventional seats capable of accommodating the cast. All seats were installed per the manufacturer's instructions. As a control, tests were performed without a cast using the conventional/standard seats. Results: The lowest overall loading of the dummy's head, neck, and chest occurred during tests with the standard seats. While it was easier to seat the casted child in the spica-specific seats, these designs led to greater loading on the dummy's body. In a spica-specific seat, the chest acceleration values exceeded the federal limit in a test where the seat was installed in a reclined orientation that was within the manufacturer's described positioning. Conclusions: Spica-specific seats more easily accommodate the cast, but conventional seats can provide similar levels of protection in a crash. As cast and seat designs continue to evolve, hospitals might consider having a range of seats available for patient use. It is important to help caregivers make informed decisions on how and when to transport children with hip spica casts.