OBJECTIVE: The China Seven Cities Study (CSCS) monitors geographic and temporal trends in tobacco use among adolescents and adults in seven cities throughout Mainland China: Harbin, Shenyang, Wuhan, Chengdu, Kunming, Hangzhou, and Qingdao. This article presents the methodology and prevalence data from the baseline survey of the CSCS, conducted in 2002. METHODS: Stratified random samples of middle schools, high schools, and colleges were selected within each city. Students and their parents completed self-report surveys of their tobacco use. Data were obtained from 6138 middle school students, 5848 academic high school students, 2448 vocational high school students, 2556 college students, and 25 697 parents. RESULTS: Smoking prevalence varied across age groups, school types, genders, and cities. Past-month smoking prevalence was 9% among middle school students, 8% among academic high school students, 26% among vocational high school students, 21% among college students, and 40% among parents. Smoking prevalence was higher among males than among females, with larger gender disparities among adults than among youth. Smoking also varied across cities, with higher smoking prevalence in southwestern cities and lower prevalence in coastal cities. Intraclass correlations of students within schools are presented to inform statistical power estimates for further research in China. CONCLUSIONS: These results provide a baseline for future longitudinal studies of smoking in these cities and identify demographic groups at risk for tobacco-related disease. Effective smoking prevention programmes for youth and smoking cessation programmes for adults are needed in China, especially in the lower-income southwestern cities and in vocational high schools throughout the country.