In the United States, 73% of all deaths among youth and young adults 10-24 years of age result from only four causes - motor vehicle crashes (30%), other unintentional injuries (10%), homicide (20%), and suicide (13%). Substantial morbidity and social problems also result from the approximately 1 million pregnancies that occur each year among adolescents as well as the estimated 3 million cases of sexually transmitted diseases (STDs) that occur each year among the same age group.