Adult smokers were found to reduce cognitive dissonance regarding their smoking behaviour by adhering to rationalizations or justifications to continue smoking, also known as disengagement beliefs. These beliefs were found to be an important barrier with regard to smoking cessation practices. Neither the occurrence of disengagement beliefs, nor its effect on motivation to quit and actual smoking cessation have been studied among adolescent smokers. Therefore, this prospective study among a sample of 363 adolescents examined the extent to which adolescents adhere to disengagement beliefs, and the relations between disengagement beliefs and adolescents' motivation to quit smoking, motivation change and smoking cessation. The association and interplay between disengagement beliefs and level of nicotine dependence was also assessed. Results showed that the degree to which adolescent smokers adhere to disengagement beliefs was similar to that of adults, if not stronger. Higher levels of dependence coincided with stronger adherence to disengagement beliefs. Further, when controlling for nicotine dependence, disengagement beliefs were strongly negatively associated with motivation to quit, but only marginally inversely associated with smoking cessation one year later. Nicotine dependence was the strongest barrier for smoking cessation at follow-up.