Passenger restrictions for new teenage drivers that became law in 1998 in California provide an opportunity to study the effectiveness of such laws in reducing the number of passengers as well as the influence of teenage passengers on novice drivers. Using fatal and injury crash data from California's Statewide Integrated Traffic Records System, this study found that teenage passengers are a causal factor in crashes of 16-year-old drivers and that in the three years following implementation of the new law, the average number of teenage passengers carried by 16-year-olds decreased by approximately 25%. Without considering the beneficial effect of a decrease in the crash rate, the decrease in the number of teenage passengers in actual crashes resulted in an estimated saving of eight lives and the prevention of 684 injuries over a three-year period.