We compared 1,335 adolescent smokers and quitters from six European countries with regard to attitudes toward smoking, self-efficacy, social influences, and intentions to quit smoking. At 6-month follow-up, occasional, weekly, and daily smokers who had quit indicated less social influence of friends and siblings toward smoking, acknowledged more disadvantages of smoking, and expressed more confidence that they would be able not to smoke in various tempting situations. Logistic regression analyses revealed that smoking status at baseline and social influence of peers were the main predictors of cessation. Although no large cultural differences were found, the pattern of predictors was not similar for all six countries. As adolescents who smoke regularly are less likely to quit, strategies to prevent them from taking up the habit are important. The influence of peers calls for inclusion of peer groups in cessation strategies.