To evaluate the California Child Passenger Restraint Law requiring children under four years of age to be transported in car seats, we examined monthly injury and fatality levels from January 1978 to December 1983 for children 0-3 and 4-7 years of age using Box-Jenkins time series models. A significant 8.36 per cent reduction in injuries was found for the 0-3 year old age group, but no significant reduction in injuries was found for 4-7 year olds. No significant reduction in fatalities was found for either age group. A similar analysis of injuries and fatalities in Texas, a state without a car seat law, showed no significant reductions in either injuries or fatalities. There was no change in the number of California 0-3 year olds in the years after the law was enacted.