Little is known about the best ways to help young people stop smoking. Bupropion (a medication marketed as Wellbutrin or Zyban) has proved helpful in treating adult smokers. The purpose of this study is to determine if bupropion is also effective in treating smokers between the ages of 12 and 25 years old. This study also compares the effectiveness of bupropion used as a supplement to behavioral treatment versus behavioral treatment used alone. In addition, the study evaluates whether hormonal response to stress measured prior to the start of treatment predicts whether individuals respond well to treatment with medication.