Public Health (1991), 105,425-433 © The Society of Public Health, 1991 Change in Children's Smoking from Age 9 to Age 15 Years" The Dunedin Study W. R. Stanton 1, P. A. Silva 2 and T. P. S. Oei 3 7Research Fellow/Biostatisticbn, Dunedin Multidisciplinary Health and Development Research Unit, Department of Paediatrics and Child Health, University of Otago Medical School, Dunedin, New Zealand; 2Director, Dunedin Multidisciplinary Health and Development Research Unit; 3Director, Clinical Training Program, Department of Psychology, University of Queensland, St Lucia, Queensland, Australia, 4067 Studies have shown that the rate at which children take up smoking is still very high, particularly for female adolescents. While some progress has been made in determining the factors related to the initiation of smoking, an issue that still requires investigation is the relationship between early smoking patterns and later smoking behaviour. This paper reports the results of a longitudinal study which examined the continuity between smoking at an early age and later smoking behaviour. The smoking behaviour of a cohort of New Zealand children was followed from age 9 to age 15 years. Results showed that children's smoking pattern at age 9 years was not highly related to their smoking behaviour at age 15. The children most likely to become daily smokers by age 15 were those who had smoked within the last year at ages 11 and 13. It was concluded that the formative period for children's daily smoking at age 15 was from 10 to 13 years of age. Introduction Studies of children's smoking have shown different patterns of change in prevalence rates for different countries. This partly reflects the level of success in reducing the number of young people taking up smoking, or reducing the amount they smoke. Results of a recent study ~ conducted on behalf of the Tobacco Institute indicated that among ll-year olds the prevalence of smoking at least once a week was about 1% in Australia, New Zealand and England, and 4% in Canada. The prevalence of smoking at least once a week among 15-year olds was reported as 19% in Australia, 22% in New Zealand, 28% in England and 35% in Canada. Cross-sectional studies, which provide prevalence rates for children of the same age in different birth cohorts, show generational changes in smoking behaviour, and extension of this research design to a number of age groups can show trends across age. However, such studies do not show the extent of continuity and change of smoking habits among individual young people. In addition, concern about possible underestimation of the prevalence rates has been directed mostly at cross-sectional studies 2 (but also toward data from longitudinal studiesS,4). Correspondence: Dr Warren Stanton, Dunedin Multidisciplinary Health and Development Research Unit, University of Otago Medical School, PO Box 913, Dunedin, New Zealand.