Data is required on the motivational determinants of smoking cessation among a multi-ethnic sample of adolescents in South Africa. The I-Change Model was used to explore the determinants of smoking cessation among a sample of 1267 Black African, Colored and White Grade 9-11 monthly smokers and former smokers in the Southern Cape-Karoo region. Across the ethnic groups, former smokers displayed a more positive attitude toward non-smoking, were surrounded by a social environment that was more supportive of non-smoking, displayed higher self-efficacy not to smoke in stressful, routine and social situations, and were more positive about their intention not to smoke in the next year. The I-Change Model can be used to address the cognitions of smoking in a multi-ethnic society like South Africa. However, some ethnic tailoring will be required. Black African students will benefit from a focus on attitudinal cognitions and cultural factors that motivate smoking. Colored students require the involvement of their social environment, while White students will benefit from the development of refusal skills in social situations.