Tobacco control programmes in multi-ethnic societies must take into account ethnic differences in the determinants of smoking. The I-Change Model, an extension of the Theory of Planned Behaviour, was used to investigate the factors related to smoking among a sample of 3378 Black African, Coloured and White, monthly and nonmonthly smokers in the Southern Cape-Karoo Region, South Africa. Across the ethnic groups, non-monthly smokers reported a more positive attitude towards nonsmoking, social influences that were more supportive of non-smoking, higher self-efficacy in stressful, routine and social situations, greater intention not to smoke in the next year and lower levels of depressive mood and risk behaviour. Regression analyses suggested that the weight of these determinants may differ in predicting monthly smoking among the ethnic groups. Black African students may benefit from the development of attitudinal cognitions and coping skills to counter peer influence. Coloured students also require skills to resist peer influence. White students require coping skills in stressful and social situations. Although there are more common than unique determinants of smoking among South African adolescents, further research is needed to understand the influence of differing social, economic and cultural contexts on smoking onset.