Teen smoking has serious long-term consequences, including the risk of teenage smoking-related diseases and the risk of premature death, as well as causing increased health care costs associated with treating the illnesses. Any adults who are addicted to tobacco today began smoking as adolescents, and it is estimated that more than 5 million of today's underage smokers will die of tobacco-related illnesses. These consequences underscore the importance of studying patterns of smoking among adolescents.